text:
Effect of doubling volumes of PCR reagents
We ran PCR with a positive control and two lanes of sample. We used the same sample, but in one PCR mixture we used a total volume of 50μL (25μL Taq, 5μL forward&reverse primer each, 10μL sample, 5μL dH2O) while in the other we halved each volume to a total of 25μL. Pipetting was done by the same person.
The positive control and the 25μL total volume lane gave nice and clear bands, but the 50μL sample showed nothing. How could this be explained?
Edit: We only ran one PCR with all the samples simultaneously, so no second thermocycler or different temperatures or anything. Didn't even consider that option!
Edit 2: In case it's relevant, we were using this: http://www.chemheritage.org/discover/collections/collection-items/scientific-instruments/perkin-elmer-cetus-model-480-dna-thermal-cycler.aspx

Could you attach a picture of the gel? Also, how many times was this experiment repeated? I have used different volumes many times with no difference in efficiency (but with Phusion polymerase)

The thermal cycler adjusts sample temperature based on the volume of the sample. So if you run samples of different volumes side by side, not all of them will cycle through the optimal temperatures of each step. If you were working with a "hot start" polymerase this is even more critical, as the Taq won't be able to amplify at all unless the sample is heated up to a specific temperature.

But presumably, @Armatus used different thermocyclers and he entered the appropriate volume of the sample in the thermocycler options.

@GerganaVandova I didn't presume either that they did or didn't. In both cases it's still a probable reason for this problem. I imagine an ideal set of answers as all probable reasons for a problem. Then anyone looking this up in the future could use the answers to troubleshoot.

Does this apply to very old models? How would the thermocycler test the volume in a tube or the temperature it reaches? We weren't using a hot start.

Older models simply raise the block to the temperature and don't worry about controlling for getting the liquid in the tube to the indicated temperature. In this case, it is possible that the real temperatures were different depending on volume.

That sounds like the most likely problem; I think you should post that as an answer.


text:
Cell cycle selection
Is it possible to select from colonies only cells which are at a certain stage in the cell cycle? E.g. if I was trying to analyse expression of a number of genes during different stages of the cell cycle.
I could imagine that if this is possible, the selection mechanism might target cyclins, or use an artificial gene cassette controlled by them.
So for example, a method may attach some gene to a certain cyclin which protects against a substance that otherwise destroys the cell. We could then use that substance to destroy all cells which were not in the cell cycle stage that we want to look at, wash away their nucleic acids, and then extract the mRNA from remaining cells to analyse expression levels at this particular stage in the cell cycle. If we repeat that for the different stages, we should be able to get a nice picture of what is expressed when. Does any method like this exist or is commonly used?

see http://en.wikipedia.org/wiki/Cell_synchronization and http://en.wikipedia.org/wiki/Synchronous_culture

Depending on the stage of cell-cycle you are interested in, people often use the size/morphology of the cell as an indicator. Then you select cells with a cell sorter.
Another option is to specifically tag some cellular molecule that can give an indication as to the relevant stage and then sort the cells based on the tag. This does not necessarily have to be cyclins - for example if you are only interested in S/G2 you could tag the DNA or maybe histones.

Hoechst fluorescent DNA stain permeable to live cells can be used with a cell sorter to distinguish between G1, S & G2/M populations, resolving the sorting of the third G2 & M being the complication unless an specific Mitotic surface marker is used as this sub-population tends to be the most scarce at a given time in an asynchronous cell cycle mix-population of cells, thus the tendency to enriched for mitotic cell content but shake-off etc.

You have correctly stated that we can monitor cell cycle stage by either monitoring protein (cyclin) levels or by following indirect methods such as green cassettes. One usually tries to monitor changing levels of:

G1 cyclins (D cyclins)
S-phase cyclins (cyclins E and A)
Mitotic cyclins (B cyclins)

Or one might try to modify the gene where these proteins are produced so that one can observe some unique behavior that highlights that particular stage of cell cycle is going on.

Thanks for the info! Though it doesn't quite answer what I wanted to know - I added more detail to my question as I can understand that I was a bit unclear.

The only strategy close to your suggested description is based on FUCCI sensors.
Fluorescent markers designed so that their presence informs of specific stages of the cell cycle, in principle without disrupting or perturbing cell progression.
So, although there is not a physical clean-up of pure cell sub-populations, these can be tracked by the abundance of these markers and even isolated by FACS.
I guess the issue of developing something selectively "lethal" (which does exist in the context of certain plasmids transformed in E.coli) lies partly in being able to retrieve those surviving cells in a timely fashion so that being halted at that particular stage is not detrimental. It does sound as an interesting analogy to Sanger Sequencing where 4 different terminators of each of the 4 bases render truncated fragments easily readable. In principle within the context you suggest, a single cycle would be allowed post genetic manipulation (eventual silencing of such genetic modification as representing an undesirable weight for the cell would be expected otherwise). As progression through each phase varies substantially in time, the idea in itself would require substantial refinement, and most likely the use of a conditional expression system. In this way a mix population transfected with the specific set of markers could be triggered for expression at a given time and then monitored for negative selection.
Commonly though, chemical synchronisation or perhaps more physiologically relevant methods of separation like elutriation, aim at enriching cell populations at specific stages of cell division. Mitotic cells are particularly problematic being rather scarce at any given time within an unperturbed population of growing cells. Mitotic shake-off followed by addition of hypotonic solutions have been suggested as methods of mitotic retrieval but yield is comprehensibly low.

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text:
Is there any antibody-forming immune system without immunological memory?
Is it possible for an immune system to exist that makes antibodies but does not possess any kind of immunological memory? If so, what examples are there?

have you tried googling this?

@aaaaaa yes, but I couldn't find the answer of my question.

Disagree with the close votes. This may not be a particularly sophisticated question but it's certainly within the scope of biology.

There is no system that makes antibodies but that doesn't have memory.
The title of this question is was originally very different from the body. The title asks if there's "any immune system without immunological memory", while the body asks if there's "any immune system that makes antibodies but has not immunological memory". That suggests you may think that antibodies are an essential part of an immune system, or that immune systems comprise only antibodies. Neither is true. The vast majority of animals have immune systems that do not have antibodies and that do not have immunological memory; for example, arthropods, the various kinds of worms, etc.
Immunological memory is a relatively recent addition to the immune system, having arisen approximately 400 million years ago, in the lineage that originated with shark-like fish.  The species that evolved from sharks -- fish, amphibians, reptiles, birds, mammals -- all have immunological memory, and all have antibodies. Those species that didn't arise from that lineage do not have antibodies, and with two exceptions do not have immunological memory.

The origins of vertebrate adaptive immunity

The exceptions are lampreys and hagfish, which have a common ancestor with sharks but which ended up forming an immune system that is related to, but often quite different from, that of sharks (and us). Lampreys and hagfish have molecules that are not antibodies but that function in a similar way, including having a form of immunological memory, though it's quite different from ours. So if you're looking for an example of something that kind of has antibodies but that kind of doesn't have immunological memory, that's as close as you're going to get.

Lamprey Immunity Poised to Evolve
Harnessing 450 Million Years of Evolution: Lamprey Antibodies for Modern Biomarker Technology

Note that virtually all species, including mammals, have branches of the immune system that don't have immunological memory. Those branches don't have antibodies, though.

Innate Immunity
The innate and adaptive immune systems

I’m not sure I agree with your characterisation of immunological memory as recent. I couldn’t find its evolutionary age with a cursory search but for all I know CRISPR (an immunological memory) could well be ancient. Similar for other cell-based immune mechanisms that rely on integration of foreign genetic material.

I don't really accept that CRISPR is "immunological memory" other than in semantics.

Huh. How is it not?

Any argument that it is relies on semantics and definitions. I don't find that an interesting game to play. Bacteria may have "immunity", but they don't have "immune systems". I'm not saying you can't call it "immunological memory" if you want, I'm just saying that I don't call it that and I don't find attempts to shoehorn it into the same category to be at all interesting.

I’m not playing semantics games. But we do seem to have different definitions. There are different kinds of immune systems, and I wasn’t aware that there was a consensus(?) that bacteria’s immunity wouldn’t count as an immune system. In fact, I know researchers (apart from me) that would call it an immune system (and it’s trivial to find publications supporting this). So what about RNAi then? Is that also not an immune system? Because, once again, I know that others call it an immune system. I don’t think your definition has special status.

I’m not playing semantics games. But we do seem to have different definitions. That's what semantics means. Really, I don't want to make a big deal of this. What I'm saying is that bacterial "immunity" is so utterly different from animal immunity that there's virtually no biological insights to be gained from grouping them together. The dictionary certainly lets you do that, but there's no biological utility to it. It's like asking if a virus is alive. It tells you about the word "alive" but nothing about viruses. It's not (biologically) interesting.

Well “games” suggests that I’m baiting you but I’m not — rather, I simply don’t understand you. Your last comment clarified that somewhat although now I could complain about eukaryotic chauvinism (but I shan’t!).

thank you for your very specific answer. actually I already knew the broad-brush concept of the innate,acquired immunity, I'm sorry for confusing you. it's very interesting that there are such unusual  type of immune system(Lampreys,Hagfish) that you mentioned.

actually I was just wondering and thinking what if there wasn't immunological memory, then how would the immune system evolve, would it just increase its diversity of antibodies or would it decrease its delay time to activate and prepare acquired immunity system, are they two trade-off relationship etc... so these are the reason why I asked the question. anyway, thank you!

@Mr.Konrad Rudolph Thank you for proofread My informal and silly english grammar!

There seems to be some evidence of immunological memory in insects. See this article, for example.

I wrote about that article, and others, on my blog in 2007: Invertebrate memory, or wishful thinking?; also here, here, and here. TL;DR, very unlikely to be real immunological memory.

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text:
How to find the amino acid that is bound to a tRNA with the anticodon?

What amino acid is bound to a tRNA with the following anticodon: $5^{\prime}$ A U G $3^{\prime}$

The answer is Histidine.

What amino acid is attached to the tRNA with the following anticodon $5^{\prime}$ A G C $3^{\prime}$

The answer is Alanine.

I also referred to this image below but unable to get the answer. Can anyone please explain how to solve this?

Each tRNA brings a single amino acid and add them to the growing peptide strand. The tRNA has an 'anticodon' which recognizes a codon on the mRNA code. How this occurs:
How to figure it out:

You have to find out the complementary bases. With DNA, A is complementary with T, and C is complementary with G. However, we are working now with RNA! It's similar with RNA, with one exception: in RNA, U (uracyl) is used instead of T, so A is complementary with U. C is still complementary with G.

Notice that the 5'-3' anticodon is antiparallel to the codon (one is 5'-3', the other is 3'-5'). This means that to find out which amino acid is being added, you have to reverse the code found on the tRNA.

Your questions, let's go step by step:

1) tRNA anticodon: AUG
tRNA complementary strand would be UAC. Reverse to get the 5'-3'
direction on the mRNA. The reverse of UAC is CAU, which is His
(histidine).

and

2) tRNA anticodon: AGC
tRNA complementary strand would be UCG. Reverse to get the 5'-3'
direction on the mRNA. The reverse of UCG is GCU, which is Ala
(alanine).

You can also reverse first and complement second. The order does not matter, provided you do both. Always visualize the process, it helps tremendously.
Let's do a final exercise to see if you understand, but in reverse and with some extra thinking. What are the tRNA sequences which bind to the mRNA strand ACUACAGUAUAC? What is the peptide sequence it will produce?
mRNA: ACU ACA GUA UAC
We can use the translation table immediately; it is used to translate mRNA into peptides directly. We find out it produces the peptide: Thr Thr Val Tyr
Reverse mRNA:  CAU AUG ACA UCA
Complement it: GUA UAC UGU AGU
(FYI: by convention, we always write mRNA in the 5'-3' direction)
The tRNA anticodons which bring (i) Thr (ii) Thr (iii) Val (iv) Tyr to build the peptide chain are (i) GUA (ii) UAC (iii) UGU and (iv) AGU.
All of these sequences are written in the 5'-3' direction, as per convention. It's easy if you are careful and clear in your working :-)

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text:
Does sleeping fewer hours than needed cause common cold?
Does sleeping fewer hours than needed cause the common cold? If so, how?

The question can be interpreted ambiguously: 1) literal meaning, sleep deprivation causes common cold, or 2) sleep deprivation causes "common cold"-like symptoms. (1) has been answered with weakened immune system and virus, though it'd be interesting to see if someone can explore on case (2), moreover if it's not caused by external source.

Technically speaking, no. Common cold is caused by a virus. Practically speaking, as the answers show, lack of sleep makes you more vulnerable to any virus.

Generally the answer to “does X cause cold” is “no, unless X is rhinovirus”. In particular, cold doesn't cause cold...

There have been some studies directly linking sleep deprivation to increased risk of catching a cold  ("Behaviorally Assessed Sleep and Susceptibility to the Common Cold Sleep". 2015;38:1353–9.).
Colds are caused by a family of viruses. There is pretty solid evidence that sleep deprivation has a significant weakening effect on your immune system. Given a weakened immune system, it would be more likely that you would catch a cold if you are exposed to one of the cold-causing viruses.

Though it would be not just colds, but any infectious disease.

@jamessqf Sure, but that wasn't the question. The first reference looks specifically at the common cold, the second reference looks at the general issue of weakened immune system.

It's a matter of correctness, I think.  If the question is simply whether sleep deprivation causes colds, then the answer is no.  Rhinoviruses cause colds.

@jamesqf And next time a rabid dog bite does not cause rabies, the virus does?

It is a similar thing as with https://biology.stackexchange.com/questions/5445/why-does-the-cold-make-us-sick?r=SearchResults Even a small child knows that a virus causes the disease. The point is whether cold temperature of nose and throat or sleep deprivation do or do not open the way for the virus to overcome the immunity becase in a typical city in the right season there is no lack of the virus. Just saying - not a disease is caused  by a virus so everything else must be a myth is just wrong. One should adk, would I be sick if I didn't get cold or if I slept more?

@jamesqf What actual point are you trying to make? The answer explicitly says "Colds are caused by a family of viruses" and refers to "cold-causing viruses". It explicitly says that lack of sleep weakens the immune system and that this makes it more likely to catch a cold. OK, it doesn't explicitly say that a weakened immune system also makes it more likely that you'll catch any other infectious disease, but isn't it obvious enough that it doesn't need to be said? Are you just upset that the answer doesn't include the one-word summary, "no"?

@Vladimir F: You might get rabies from a dog bite, but you are (in the US) much more likely to get it from raccoons, bats, and other wild animals: https://www.cdc.gov/rabies/exposure/animals/index.html  Conversely, only a miniscule fraction of people bitten by dogs get rabies, because almost all dogs are given rabies vaccines.  So dog bites do not cause rabies, getting bitten by any mammal with the disease does.  Likewise, lack of sleep does not CAUSE colds, it may weaken the immune system and make you more susceptible to infection by ANY virus - perhaps even rabies.

I think everyone agrees that "causes the cold" is imprecise language, and "causes increased chance of catching a cold" is a more precise but also pedantic way to say it. There's no point in arguing semantics any further.

@jamesqf: We can use Aristotle's causes here. The Rhino virus is the material cause; sleep deprivation is the formal cause. In general, many things happen for a combination of causes.

@jamesqf If you want to be super semantic about it, the entire set of spacetime within the OP's past Cauchy horizon caused his cold.

A new study published in this week's journal SLEEP finds that people who sleep less than six hours are more likely to catch a cold. Researchers tracked 164 healthy men and women for a week at a time, monitoring how much they slept and exposing them to the rhinovirus, also known as, the common cold.
Aric Prather, lead author of the study, and his colleagues found that those who slept less than five hours were 4.5 times more likely to have a cold than those who slept seven hours.
Only 18% of those who slept six or more hours got a cold, while 39% of those who slept less than six hours got the virus.
According to the Centers for Disease Control and Prevention, most adults average two to three colds a year and kids have even more.
Prather pointed out that when we don't sleep enough, it may impact our immune systems in a variety of ways -- from how the cells act to enabling our inflammation pathways.

I take it the baseline for control was around 13% had a cold?

How has the cold virus survived for so long? Is it able to lie dormant within a host until their immune system is weaker than normal? More people seem to get a cold in the winter.

@PaulMcCarthy Generally diseases likes colds survive by circling through large populations, and mutating quickly enough that you don't have much resistance to it by the time it comes back around to you.

@azurefrog Yes but more people appear to get a cold in Winter. If the virus was just circulating, roughly the same numbers of people would have a cold all year round.

authors: Vladimir F Героям слава


text:
What is the standard deviation of adult human heights for males and females?
The wikipedia article on human height reports mean height for many different countries by sex but it does not report standard deviations.
What is the standard deviation of adult human heights within sexes?
Obviously the size of the standard deviation would vary across countries and by other factors.  That said, I think good data on a few representative countries would be sufficient to get a reasonable sense of what it typically is and the extent to which the standard deviation varies.

It's probably around 7 cm for men and 6 cm for women.
The Evolution of Adult Height in Europe, which is a source for some of the statistics reported on that Wikipedia page, gives averages, standard deviations, and sample sizes for both sexes across 10 european countries (and across a number of different age cohorts).
Taking their numbers for men and women born between 1966 and 1978, the average male standard deviation of height across all ten countries is 7 cm (range 6.7-7.3) and female 6.1 (range 5.6-6.4).
For a more global context, Subramanian et al. give heights with standard deviations for a much wider selection of countries, mostly "developing countries". Unfortunately for your question, they only report numbers for women. However, these  look pretty similar to the Europe numbers: the across-country average SD for women is 6.3. (with all these countries, the range is greater at 5.4-8.1, but 32 out of the 54 countries have SDs within the Europe range for women, i.e. 5.6-6.4)
Note: for this estimate I just ran averages across years/countries, I didn't weight the averages by sample size.

 Subramanian SVS, Özaltin EE, Finlay JEJ. 2010. Height of nations: a socioeconomic analysis of cohort differences and patterns among women in 54 low- to middle-income countries. PLoS ONE 6: e18962–e18962.

The first link is broken now, btw


text:
Good book on Origin of Life
What is a book that goes into reasonable detail (but isn't textbook-level technical) about the origin of earth and in particular the origin of life on earth? Something intended for a broad audience, but that still covers the biology/geology and does not completely gloss over the sicence.

I think this may be way too broad.  Are you able to narrow down your interests any further?

I would recommend The selfish gene by Richard Dawkins. It is targeted at a scientifically interested audience, but well written and recognized by the scientific community.
http://amzn.com/0199291152

I think this book (The Story of Life, Southwood) would be just what you are looking for - it was one of my modules during my undergrad in Evolution and I think it touches on the basic geology too. It is quite an easy ready but covers the material pretty well, it also has good reviews on Amazon etc.

This book by Steven Rose is supposed to be an update of the original for a modern audience:
http://www.amazon.co.uk/Almost-Like-Whale-Species-Updated/dp/055299958X

I think you mean Steve Jones. Steven Rose wrote The Chemistry of Life.


text:
Is there a consensus on whether or not race exists on a biological level?
The most recent survey I could find was from 1985 which said that 16% of biologist disagreed that "[t]here are biological races in the species Homo sapiens."
I was wondering if there's been a change in this position.

What, only 16%? That’s markedly different from the consensus that I’ve experienced so far, which is almost unanimously against a meaningful biological basis of races.

possible duplicate of Do humans have enough biological differences to be grouped into races or subspecies?

@GoodGravy Thanks for the link. Wasn't around when I asked.

This has been investigated extensively on skeptics.stackexchange.com.
Unfortunately, it’s not easy to determine a scientific consensus since nobody has cited a relevant survey. On the other hand, here are some salient quotes from scientific literature (stolen from the answers to the above-mentioned question) which I find worth repeating:

A subspecies (race) is a distinct evolutionary lineage within a species. This definition requires that a subspecies be genetically differentiated due to barriers to genetic exchange that have persisted for long periods of time; that is, the subspecies must have historical continuity in addition to current genetic differentiation. [Templeton, 1998], cited in [Long & Kittles, 2003]

Which speaks against the existence of races as a meaningful biological concept.
On the other hand, Jorde & Wooding (2004) contend that,

Genetic variation is geographically structured, as expected from the partial isolation of human populations during much of their history. Because traditional concepts of race are in turn correlated with geography, it is inaccurate to state that race is "biologically meaningless".

But they concede that

there is no scientific support for the concept that human populations are discrete, nonoverlapping entities.

Finally, it’s worth noting that in the universally agreed-on taxonomy, formalised in the International Code of Zoological Nomenclature there simply is no category for races, whether they would make sense or not. Whether or not this view enjoys a majority vote in biology, it’s the de facto consensus.

Jeffrey C. Long & Rick A. Kittles, Human Genetic Diversity and the Nonexistence of Biological Races, Human Biology 75 (4), pp. 449–471, Aug 2003
Lynn B. Jorde & Stephen P. Wooding, Genetic variation, classification and ‘race’, Nature Genetics 36, pp. 28–33, 2004

Anatomically modern humans are less than 200K years old, left Africa (or possibly Africa and Arabia) only 60K years ago, and migrate quite a lot (think of the Mongol invasion).  So you would not expect to have clear divisions into subspecies.  And indeed a quick search of google scholar pulls up no claims in the literature for human subspecies of anatomically modern humans (i.e. no subspecies of homo sapiens since Neanderthals and Denisovans).
On the other hand, it's certainly the case that you can work out a rough phylogenetic tree of humans.  Native americans are descended from certain northern and eastern asians, and so in the 1400s were more closely related to them then they were to other humans.  Similarly, Austronesians (of Indonesia and Polynesia, e.g.) are more closely related to Taiwanese aborigines than they are to Australian aborigines.  This tree is complicated by how much more migration there has been in the last 1000 years than there was previous to that, but it's still biologically meaningful.
But here's the striking thing: traditional notions of "race" do not match up well with this tree.  The deepest and most fundamental phylogenetic splits in the human tree are within Africans.  If you were going to try to "scientifically" come up with races, you'd end up with something vaguely like one for Khoisan, one for other Africans, and one for all non-Africans.  Even ignoring modern admixture, traditional races are not monophyletic.  Any clade including all "black" people includes all people, any clade including all "east asians" includes all native americans.  (Also note that traditional notions of "race" are not stable over time, remember that "Irish" used to be a "race" on the US census.)
Modern admixture even more clearly shows the non-genetic nature of traditional "races."  One genetic study of people who identify as African-American, found that African ancestry can be as low as 1% and as high as 99%, with the median African-American having 18.5% European ancestry (with 30% having European y-dna).  Furthermore, relatively ancient admixture (for example, in the Northern Africa, Northeastern Africa, Middle East region or in Madagascar) also complicates the situation significantly.
To summarize, although human genetic diversity is a real biological phenomenon which can be used to figure out the geographical history of people's ancestors, traditional notions of race do not match up well with the biologically meaningful concepts.

Sounds like the overlap is so great that such a description would have so many races that a couple of these answers use the word meaningful.

Its not known what the consensus is but there is definitely a decline in the race concept.
"The concept of biological race has declined significantly in frequency of use in physical anthropology in the United States during the 20th century. We present three kinds of evidence of this rejection of what was a core concept: (1) The frequency of articles using the race concept in the AJPA declined from 60 percent in 1918 to 4 percent in 2001 (r = -.89, p = .01). (2) Content analysis of university level textbooks of introductory physical anthropology for 1980-99 found only one textbook which supported the race concept. (3) A series of mailed questionnaires to members of the American Anthropological Association found that while 37 percent of responding physical anthropologists rejected the race concept in 1978, this rose to 69 percent in 1999.”
Section - Summary, paragraph 1
"The decline of race in American physical anthropology"


text:
For each movement performed by both the gluteus minimus and medius, what percentage of the movement do the gluteus minimus and medius account for?
From what I read on Wikipedia, all functions of the gluteus minimus are mirrored by the gluteus medius. Additionally, the gluteus medius is larger than the gluteus minimus (see comparative images here), which leads me to believe that the gluteus medius is stronger than the gluteus minimus. I wonder to what extent it is stronger.
For each movement performed by both the gluteus minimus and the gluteus medius, what percentage of the movement do the gluteus minimus and the gluteus medius account for, respectively? (e.g., 80% of the strength stemmed from the gluteus medius, and 20% of the strength stemmed from the gluteus medius)


text:
Do any animal have a tendon repair process that is more efficient than in humans?
Tendon injuries are notoriously slow to heal for humans, and quite often do not heal properly due to a variety of reasons. Do any animal have a tendon repair process that is more efficient than in humans? Efficient = faster + higher repair quality. If so, what property(ies) make the  tendon repair process more efficient?

I unsuccessfully searched for "tendon repair in animals" on Google and Google Scholar.

There are vertebrates that can regenerate an entire limb. Possibly there are thousands of animals that are better than humans in tendon repair. Moreover, asking an explanation for all the factors that affect tissue healing is a broad question. You should narrow down your question a bit.

@WYSIWYG Good point, let's restrict ourselves to the animals that cannot  regenerate an entire limb. Note that while there might be a fair amount of animals in that situation, our knowledge of tendons in animals is quite far from perfect, so the amount of animals known to be in that situation is most likely much more limited, if any. E.g. we only understood quite recently that frogs jump so high thanks to their tendon properties (https://news.brown.edu/articles/2011/11/frogs).


text:
How does the structure of tendons change as they become stronger?
I understand the basic structure of tendons, but I wonder how a tendon becomes stronger via exercise. Do the collagen fibers become more aligned/numerous/dense/etc.? Is the tendon expected to become thicker as it gets stronger? Does the cellular content of the tendons somehow change (e.g., more tenocytes, or higher quality tenocytes)? What other factors have a role in tendon strengthening?


text:
What percentage of the human genome hasn't been sequenced yet? If percentage estimates aren't precise, why is it difficult to estimate?
What percentage of the human genome hasn't been sequenced yet? I have read different estimates, e.g.:

https://www.genome.gov/human-genome-project/Completion-FAQ (mirror): "In the April 2003 version, there are less than 400 gaps and 99 percent of the genome is finished with an accuracy rate of less than one error every 10,000 base pairs"
https://www.statnews.com/2017/06/20/human-genome-not-fully-sequenced/ (mirror):  "Church estimates 4 percent to 9 percent of the human genome hasn’t been sequenced. Miga thinks it’s 8 percent."

If there isn't a consensus on the percentage of the human genome that hasn't been sequenced yet, why is it difficult to estimate?

Why do you care if it is 5% or 6%? What are you going to do with the number, which in any case will probably have changed in 12 months time. That isn't an interesting scientific question, which is why you are unlikely to find a "consensus" — people aren't discussing it. What is interesting is nearer to your last question. Why it is difficult to estimate is subsidiary to the question why the remaining gaps are difficult to fill. I suggest you search for info on that (perhaps even here on SE Biology) and come back with a modified question if necessary.

@David's comment may be a bit harsh, but I think the recommendation to focus on the last sub-question as the actually interesting bit is good. Although you say there is not consensus, "4-9%" and "8%" are estimates in complete agreement with each other because 8% is in the range 4-9%. The second article you link specifically explains why this is different from the "99%" or "complete" number in your first link (99% is relative to the amount that "can" be sequenced with the technique used).

@BryanKrause I don't think that's correct: The 99% estimate and the other estimates essentially refer to the same. They are simply vastly different and contradictory estimates. In particular, the amount that “can” be sequenced and assembled has been sequenced and assembled to exactly 100%.

@KonradRudolph Further evidence that the interesting question is the one David suggests rather than the title.

This is likely related to long repeating sequences of DNA which are unlikely to be sequenced with current sequencing techniques. Essentially we cannot determine the number of repeats and thus we have to estimate how much of the DNA that remain unsequenced.

I answered a related question here that may be helpful.
Some initial notes:

Your first bullet point ("99%") is to my reading talking about not the total genome size but the data that they actually assembled- e.g. for 99% of nucleotides, we are 99.99% that the nucleotide at that position is not some other nucleotide, but there may be other positions not included in the denominator that are simply not in the assembly in the first place. In other words, the existence of the position in the assembly and our confidence of the accuracy of a nucleotide call for such a position are two different (though related) phenomena.
Also, you are comparing a 2003 estimate to a 2017 estimate. We learned a lot in those 14 years.

To answer the last and most specific question about why this number is hard to know, there are a variety of reasons why:

There is no single number that is the "actual" true sequenced percentage of the human genome. In this I strongly disagree with commenter Konrad Rudolph (technological change is now giving us telomere-to-telomere assemblies of human chromosomes! The question is not how much it's possible to sequence and assemble but more whether it's the worth the time and expense to do so.). No two genomes are exactly alike, and that means not only that the nucleotides are different but that the positions are different. So even if we sequence 100% of your genome, that may only include 99% of my genome. These variable regions are, as suggested in the comments, largely repetitive regions but also just big chunks that are missing; to learn more about this google "structural variation" (here is an older review on the topic).
As mentioned already, technological advances have changed how we view the linear sequence of the genome. Earlier estimates were limited by available technology of the time; now that we have 3rd-generation sequencing tech like nanopore and pacbio, we are learning more about the extent of our ignorance. In that sense, it is unsurprising that the denominator has changed/increased.
As commenter Jeppe Nielsen states, all of these are statistical estimates based on available data. As available data increase and the statistical models that we use to estimate change, thus do the estimated outcomes change.
Related to (1): Different populations have different chunks of genome that are unique. The initial sequencing project selected a small number of humans, who were not representative of all human diversity. Efforts to fully characterize the human pangenome are ongoing.
Sometimes contaminants sneak into genome assemblies, which have to be removed. So for every sequence in the human genome assembly, especially if it's fragmentary or recently added, there's a nonzero chance that it's not actually part of any human genome.


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Is it true that newborn babies don't produce tears while crying? Why?
Well, I was just going through an article on eye, where in fun facts it was mentioned that newly born (for initial 1 to 3 months) babies do not produce tear while crying. Actually, I have found this true.
Now, I am wondering why is it so? Does any one know the reason behind this?

See my comment here: http://biology.stackexchange.com/questions/2087/is-there-an-evolutionary-advantage-to-crying-when-sad/2100#comment2763_2100 Seems to be related to insufficient development of their nervous control (at least according to Wikipedia)

It is not completely true.  Babies develop the lacrimal system at 42 days, in utero.  The canals and ducts for tears are formed at 60 days [2].

At birth, tear production by the lacrimal gland is minimal. Normal tearing develops several days to 2 weeks after birth.[1]

Some 6% of newborns are born with a tear duct obstruction (in some online articles it stated up to 10%, but I think my source is more reliable).  The child still produces tears, but they can well up on the eyelid [2].
Other more serious abnormalities can cause this problem.  Duct cysts or hemangiomas can also cause tear duct blockages in more severe cases.  Various factors, such as anatomical abnormalities and problems with pumping tears increase the propensity for the disorder in children with Trisomy-21 [2].  As nico has alluded to in the comments, there may be a lag in the development of the physiology of tear production even in non-Trisomy-21 children.

[1] Thomas K. McInerny, MD, FAAP, ed. 2009. American Academy of Pediatrics Textbook of Pediatric Care. Elk Grove Village, IL. American Academy of Pediatrics, p1706.
[2]M. E. Wilson et al. (eds.), Pediatric Ophthalmology, 2009, pp. 276-284.  DOI 10.1007/978-3-540-68632-3_1.

This does not really answer the question of whether newborns cry without weeping. They have a lacrimal system, but that does not mean that 1) it is fully functional and 2) they use it when crying.

@nico I didn't find anything on the nervous control of the ducts other than its pathophysiology in Trisomy-21 patients.  The original question did not ask about full functionality, so I made some presumptions based on the fact that no further anatomical development occurred was noted to occur after birth.  If you find some information on the neurophysiological development, I look forward to reading it!


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What does the 34/70 in Saccharomyces pastorianus Weihenstephan 34/70 stand for?
I've searched everywhere.
No Wikipedia page.
No information on NCBI.
I searched all occurrences of 34/70 in some primary research articles!
The best I've found is this brewery forum where someone asked the same question.
And the user rockfish42  answered:

No idea why they use that number, but it's the catalog number at
  Weihenstephan's hefebank.

I went to the Yeastbank website at Weihenstephan for some info. The keyword here is "Stamm," which is German for stem, clade, clan, or strain. So, I would take this to mean that the 34/70 is an isolate (#70) of strain 34. Two of 34/70's strengths, according to the link above are it makes clean beer and gives a pleasant taste profile due to its low yeast-like aroma in the finished beer. I can attest to that firsthand, having had on numerous occasions the pleasure of partaking of Weihenstephaner beer in its home city of Freising.

I am not sure why you say there is no information... a quick Google search returned a few interesting pages...
In this paper:
Progress in Metabolic Engineering of Saccharomyces cerevisiae - Nevoigt, Microbiol Mol Biol Rev. 2008
the author says:

The identification of the entire genomic sequence of a commonly used lager brewer's yeast strain, i.e., Weihenstephan Nr. 34 (34/70), represents a breakthrough in the molecular analysis of lager brewer's yeast.

So, it would look like 34/70 is just a catalogue number, with no specific meaning.
Curiously, according to the Wikipedia page on Saccharomyces pastorianus:

S. pastorianus never grows above 34 °C (93 °F)

So, I cannot exclude the hypothesis that 34 could come from there although, well, I personally propend for the catalogue number.
Other interesting links:
The paper about the S. pastorianus genome sequencing:
Genome sequence of the lager brewing yeast, an interspecies hybrid. - Nakao et al., DNA Res. 2009
An article comparing two different strains of S. pastorianus, 34/70 and 34/78 (again, catalog number hypothesis seems to be the most obvious explanation)
Molecular species of phosphatidylethanolamine from continuous cultures of Saccharomyces pastorianus syn. carlsbergensis strains. - Tosch, Yeast. 2006
The NCBI taxonomy page (entry #520522)

That was a lot of effort for an answer that contained no new information. The question already said that 34/70 is the catalog number. The question was what the 34/70 means.
And no it is not the temperature at which it starts to grow, that would mean Stamm W 195 starts to grow at 195°C !! Larry_Parnell's answer is much better.

No, the yeast stops growing at 34, so that's most probably just a coincidence, as I said. As for the new information... your question does not contain any of this and you said there was no Wikipedia or NCBI page, so I pointed out that there are in fact such pages, that's all. If the other answer is better accept that, I surely won't be offended.

Yes my question said that it was the catalog number. See the quote. There's no wiki page for Saccharomyces pastorianus Weihenstephan 34/70, and I didn't say there's no NCBI page, just that the NCBI page didn't have any information about the 34/70. Sorry that I misread it as 'starts growing' rather than 'stops growing' , but the argument still stands the same =)


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Methods of nuclear transfection - nuclear transport
I am reading through the ENCODE papers, which is taking me well out of my comfort zone in terms of modern laboratory techniques. At the risk of asking a question which may well be thoroughly answered somewhere else on the internet, I was hoping for a brief explanation of nuclear transfection.
In Whiteld et all, they describe the direct assay of transcription factor binding site efficacy in human cells.  To do this, they transfect a luciferase plasmid, presumably into the nucleus of the cell (because they subsequently observe that the luciferase plasmid is transcribed).
Reading through Materials and Methods and getting to the supplementary file, they disclosed their transfection protocol. The relevant reagants appear to be:
FuGene 6

a nonliposomal formulation designed to transfect plasmid DNA into a wide variety of cell lines with high efficiency and low toxicity.

(From Promega's website.)
Lipofectamine LTX

efficient reagent for plasmid delivery and protein expression

(From Invitrogen's website.)
PLUS reagent

PLUS™ Reagent is used in conjunction with transfection reagents, such as Lipofectamine™, to enhance transfection in adherent cell lines.

(From Invitrogen's website.)
Apparently, the protocol is to combine the DNA plasmid with transfection reagent, wait a few minutes, and then add in the cells, and incubate at 37ºC for 24 hours. That's all that is required to get the plasmid into the nucleus.
I have consulted Wikipedia and Strachan and Read's Human Molecular Genetics 4th edition, but been unable to answer my question about this technique.
I think I have a pretty clear understanding of how these reagents are able to get through the cell's lipid membrane, but I don't have a similar understanding of how the DNA then passes to the nucleus.
In Human Molecular Genetics 4th edition, I can find only one paragraph about plasmid transfer across a nuclear membrane, page 704: "Transport of plasmid DNA to the nucleus of non-dividing cells is very inefficient because the plasmid DNA often cannot enter nuclear membrane pores. Various methods can be used to faciliate nuclear entry such as conjugating specific DNA sequences or protein sequences (nuclear localization seuqences) that are known to facilitate nuclear entry, or compacting the DNA to a small enough size to pass through the nuclear pores."
But nothing in the materials and methods section of Whiteld et. all mentions any of these techniques. I'm sure they would have mentioned if their plasmid included a DNA conjugation sequence, so that can't be it. Perhaps these reagents implicitly include some sort of DNA compaction polycation, such as PEG-CK30?
Isn't the cytoplasm an extremely hostile place for DNA plasmids? Shouldn't they just flail around in the cytoplasm until they are digested?
Or perhaps these vectors sneak into the nucleus during mitosis? (This is a theory that just occurred to me when contemplating the "non-dividing" qualification in the Strachan quote.)
Since the question isn't addressed in the paper, I can only assume the answer is elementary and something that a professional cell biologist would be expected to know. I've run out of obvious next steps for finding the answer, so I beg pardon in advance for asking it.

My attempt to find an answer has suggested that no-one knows how the DNA gets into the nucleus.
This fairly recent paper reports attempts to track the pathway of DNA entry and transfer to the nucleus.

Le Bihan et al. (2010) Probing the in vitro mechanism of action of cationic lipid/DNA lipoplexes at a nanometric scale. Nucl. Acids Res. 39:1595-1609

The technique used was transmission electron microscopy. Complexes of plasmid DNA + cationic lipids (lipoplexes) were labelled with silica-based nanoparticles to allow visualization.
The authors describe a transfection pathway with five steps:

(i) binding of the lipoplexes to the cell surface;
  (ii) entry of the lipoplexes into the cells mainly via endocytosis (a direct fusion with cell membrane cannot be excluded);
  (iii) DNA release into the cytosol;
  (iv) transport through the cytosol; and
  (v) entry of DNA into the nucleus and nuclear transcription.

The authors were able to follow each of the first four steps but:

our data show nanoparticles close to, but not within, the nucleus.

They speculate about what this might mean, but they do not refer to any previously published data. My conclusion is that the answer to your question is, as I said at the beginning of my answer: no-one knows how the transfected DNA enters the nucleus.

Thanks Alan! I'm upvoting this for the nice article summary, but leaving the question unanswered in case someone else can comment specifically on Whiteld or shed some more light.

The paper describes silicon nanoparticles in the 10 - 15 nm range, so it's not surprising they don't enter the nucleus, the nuclear pore complex won't let particles larger than about 5 nm through by passive diffusion and active transport requires a nuclear localizing peptide. Once the nanoparticles are attached to DNA liposomes, the sizes are even larger, maybe larger than the 39 nm maximum limit for nuclear pore complexes.

Zabner et al (J. Biol. Chem., 1995, 270, 18997-19007) monitored the lipid-DNA complex formation and uptake which was found to be predominantly by endocytosis. Dot blot experiment shows that cells (50% population) took up 60% of the DNA. The DNA-protein complex was observed to be deposited in the perinuclear cytoplasm and formed a series of regularly packed tubules. They also verified that the endosomes carrying the complex did not fuse with lysosome.
Some of the DNA escapes the endosome (which is a known mechanism of increasing the efficiency of endocytosis based transfections) and might be taken up by the nucleus. When they compared expression of a reporter gene upon direct injection into the nucleus and upon direct injection into the cytoplasm, no expression was observed in the latter (acc. to Capecchi (Cell, 1980) the ratio of expression is around 1000:1. PDF available on Utah Uni Website). This means that the DNA uptake by the nucleus from cytoplasm is very inefficient.
Lower amount of lipids in protein-DNA complex increases the efficiency.
Your question has been partly answered. How does all that DNA cell takes up gets inside the nucleus? It mostly doesn't. It accumulates around the nucleus. But some of the free DNA does get taken up by the nucleus. This, probably, was the starting point for Dean's group.
Vaughan & Dean (Mol.Ther., 2006, 13(2) 422-428) have proposed that the plasmids get transported into the nucleus with the help of microtubule associated motor protein Dynein. They observed that disrupting the microtubule network functionality inhibited expression. When the plasmids were injected directly into the nuclei of cells, this did not have an effect. Now, microtubules transport stuff with the help of motor proteins out of which Dynein transports stuff towards the nucleus. It was observed that inhibiting Dynein action reduced the expression. The mechanism of how dynein binds to plasmid is unknown. (I've worked with dynein; it's complicated when it comes to binding mechanisms. The whole negatively charged N-terminal is disordered.)

If you read the discussion of the paper, It'd become apparent that the process is chaotic. The more the dispersion of DNA in cytoplasm around the nucleus, the more is it's uptake by the nucleus.
There is no Nuclear localization signal involved here. Mesika et al (Human Gene Ther., 2005) have increased the efficiency of plasmid expression by binding the plasmids to a protein with NLS. This is not the natural process. Vaughan and Dean have speculated that the DNA targeting sequence (e.g. SV40, CMV etc.) binds to proteins that have NLS or have adapters to bind dynein(like, Transcription factors) which might help the plasmid uptake by the nucleus. This can also explain the sequence based differential uptake of plasmids. None of these mechanisms have been experimentally verified.
[I have also been wondering about this. I bugged a lot of seniors and scoured the net for the answers. And then I found this question. Thank you for asking]

Welcome to biology SE - you should summarise the paper a little more than you have so that the answer can stand-alone (e.g. what if the link goes dead), otherwise, it should just be a comment

This is one of David Dean's papers, they're not bad, but have been hard to replicate. He basically proposes that transcription factor binding sites on plasmid DNA binds to some transcription factor in the cytoplasm, then the NLS peptide on the transcription factor binds the whole protein-DNA complex to importin and drags it to the nucleus.

Dean likes to use the SV40 promoter region, which is 72 bases long and contains several transcription factor binding sites. I'm not sure if anyone's tried it, but it should be possible to just make a 100 base oligo that contains the SV40 sequence and fluorescently label it. See if that goes to the nucleus.

This is a question that keeps coming up now and then when PhDs or post-docs discuss transfection. A probable answer for which I do not have supporting literature is this: If you have the transfection complex in the medium while the cells are dividing, it is possible that they can enter the nucleus following mitosis when the nuclear membrane is still forming, thus giving it access to the transciption mechanism in the nucleus.

Hello and welcome to the site. Is there no supporting literature, or do you just not have it at hand? If the latter, then you are encouraged to add citations.

I don't want to add the citations myself, but this is most likely the case for rapidly dividing cells in culture. You really should find some supporting literature to improve this answer.

This could be one of the mechanisms, but does not explain the fact that the reagents above are useful for post-mitotic cells such as neurons.

@243 They may not be as useful as you think. What kind of transfection efficiencies are you seeing, and how do they compare with rapidly dividing cells using lipofectamine or PEI?

FuGene 6 and  Lipofectamine LTX are used to transfect plasmids into post mitotic neurons primary cultured. I would not say efficiency is high, but acceptable for some experiments. For example: http://www.ncbi.nlm.nih.gov/pubmed/11716945


text:
Why do stars disappear when I look at them?
I've noticed that when I'm out at night stars seem to vanish when I focus on them. I assume the reason is physiological and not astronomic. Why does this happen? I would expect that things would be more clear when I focus on them.

You might also notice this phenomenon while lying in bed, e.g. the dim glow from the illumination of a digital clock or small LED is often visible only if you look away (using peripheral vision).

When there is little light, the color-detecting cone cells are not sensitive enough, and all vision is done by rod cells. Cone cells are concentrated in the center of the eye, whereas rod cells are very rare in the center (image source):

When you focus on the star, the light is projected close to the center of the retina, where it will hit few rod cells. Thus the star appears to vanish.

citation for figure?

it's the link before the figure, I've added "image source" to the link


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Does red light preserve your night vision?
A number of companies have started marketing LED lamps that can be switched to a red mode. The claim is that red light is less harmful to one's night vision. Given that our eyes are less sensitive to red light, though, I'm not convinced that that red light is any better than dim white light. So if "equivalent" luminosity is defined where it's equally easy to, say, read a book in both light types, is there some physiological reason that red light is better than the equivalent white light?

This is a very good question.  Red light is routinely used by scientific laboratories to do low light dissections of retinas, and of course it is used in other low light contexts such as printing plate development.
In both of the above contexts, you have a clear subject: the retina being dissected or the printing plate being developed.  In the case of the printing plate the film has been designed to be specifically non-reactive to red light, so red light is used because your eyes can see it, but the film doesn't react to it.  Similarly in some scientific settings it makes sense to use red light during dissections.  Mice lack a long wavelength opsin, and therefore using a dim red light allows the experimenter to have a relative sight advantage compared to the mouse when keeping the mouse dark adapted.
But in the case you're asking about, there is no film or animal to serve as a second party.  So is there any intrinsic advantage to using red light?  As it turns out, there is.  The fovea, which is in the center of our eye and used for high acuity vision, has no rods and primarily L- or red sensitive cones.  Note the high density center area which lacks blue sensitive cones and has 2:1 red to green cones.

So by having red light present, you stimulate this area.  But red light is present in white light, too, why not just use that?  Leonardo's answer comes the closest, but it's a little off.  Red light is used because it preferentially stimulates L cones more than rods, but you are definitely not able to preserve night vision by using red light.  Why not?  Well it may look like it is possible to exclusively stimulate cones from the chromatic sensitivity figure

But that figure is 1) normalized and 2) not indicative of synaptic signal processing.  1000's of rods can converge onto a single ganglion cell, where cone convergence in the fovea can be on the order of a single cone per ganglion cell.  When it comes to perception, in order to compare the black rod line above with the red L-cone line you'd have to magnify it dramatically in size.  Practically speaking, it is nearly impossible to stimulate cone pathways without stimulating rod pathways when using a relatively broad spectrum LED that you're powering with a battery.  Maybe with a high power infrared laser.
So the purpose of using red light is to attempt to balance the activation of high sensitivity (red insensitive) rods with that of the low sensitivity (but red sensitive) cones in the fovea.  While using a similar level of rod activation with blue light, you would perceive a "blind spot" where your fovea is.
Finally, instrinsically photosensitive cells (the melanopsin cells brought up) do not factor into this processing.  These cells are activated only with extraordinarily bright levels of light, and the therefore do not enter into conversations dealing with night vision.

How can I see blue things by the center of my eye?

You're essentially a dichromat in the center of the eye, so you are blue-yellow color blind there.  That means you can distinguish blue from any color, except yellow, over a very small region.  You can find a more thorough discussion of the phenomenon by George Wald here

No, I can distinguish blue from yellow well in the center of my sight.

Center of sight here is defined as 8 minutes of arc, or about 1/8th of a degree of visual angle. It is a very critical angle, though, since it contains your fixation point.

I have no color blindness at fixation point.

Occam's razor be damned, this must be you.

@Anixx, do you have color blindness at the edge of your vision? (Answer, yes, but your brain fills it in)

@Shep I do not know about the edge, I know about the center.

@anixx, the point it that there's a lot more going on in your visual perception than the raw inputs from photoreceptors, ranging from temporal distortions to geometric reconstruction, it's hard to say definitively that you have no color blindness.

Do you disagree with this article recommending green light for night vision? http://www.astromax.org/activities/members/kniffen.htm

A year later, does anyone who understands eye biology agree with the article recommending green over red? :(

Your "2:1" link is now broken.

@endolith one more year later, I've read the article, and to me it does sound plausible. But do note the fact that was repeated there multiple times: the (scotopic) luminance of the chart must be really low, so that you, at the very least, don't saturate rods.

Another reason why red lights are now sponsorized for night illumination is because they are supposed to be safer in terms of interference on the circadian cycle. This is not related to better vision, but better health.
The mammalian eye senses the light by the conventional rode and cone cells. However, a third light-sensing cell type has been recently identified. This third light-sensor is based on melanopsin-positive cells. While rod and cone cells respond best to white, full spectrum light, melanopsin cells only respond to a specific bandwidth of blue light, in the range of 446-477 nanometers. These cells connect and regulate brain centers responsible for circadian rhythms. Therefore, during the night, blue-light exposure might interfere with circadian rhytms facilitating the onset of depression and other metabolic derangements associated with circadian cycle see another SE question. White light contains also blue light, while red light does not. This is apparently the rationale to claim that red light is less harmful. However, no clinical evidence is available to my knowledge, and the threshold of blue light required to stimulate melanopsin receptors is probably over the common night illumination.
References:

 Hattar S, Lucas RJ, Mrosovsky N, Thompson S, Douglas RH, Hankins MW, Lem J, Biel M, Hofmann F, Foster RG, et al.. 2003. Melanopsin and rod-cone photoreceptive systems account for all major accessory visual functions in mice. Nature 424: 76–81.
 Holzman DC. 2010. What’s in a color? The unique human health effect of blue light. Environmental health perspectives 118: A22–7.

Very interesting, so a white light may mess up my sleep patterns? So is the answer to the night-vision question "no", "maybe", or "inconclusive"?

As I understand it, I would summarise this as "probably - maybe not your sleep pattern but your sleep quality will probably be affected".

@Armatus, I agree that it will probably affect my sleep patterns, but this answer says nothing about night-vision, that's what I'm curious about.

Thinking about it, since our eyes are closed - wouldn't any light become red-ish anyway because it would go through our (blood-filled) lids?

@Shep 1) sorry I'm not aware about consequences on night-vision, are companies selling red lamps claiming improvements on night-vision? 2) Red light is the only one passing through our tissues, but lamps are used after sunset when you are still awake.

@GianpaoloR, I don't want to turn this into a camping gear (or advertising) discussion, but yes, they are.

-1, sorry. This is a nice answer, but it's not an answer to the question asked here.

-1 here as well, intrinsically sensitive ganglion cells require an outrageously large amount of light to activate them.  They are not, at all, relevant to a discussion about night vision.

For the negative votes: thanks. I edited the answer to be more on target.

As mentioned in the other answer, red light does not affect the melanopsin receptors in eyes. These receptors not only regulate body rhythm but also regulate the diameters of the eye pupils. Once they are stimulated, the eye thinks that there is enough light around and the pupils get smaller to protect the eye against over-exposition, which reduces sensitivity.

any references for for melanopsin--pupils link?

In the linked article: "In the mammalian retina, besides the conventional rod-cone system, a melanopsin-associated photoreceptive system exists that conveys photic information for accessory visual functions such as pupillary light reflex and circadian photo-entrainment. "

There are multiple ways that pupils can be dilated, and this one only comes into play with very very bright light.

Yes red light is useful IF and only if >650 nm. Some of the answers above are close, but they miss the issue because they used the same scale for rods and cones which they are not on. Rods are several orders of magnitude more sensitive than cones and hence why the graphs above make it look like they have no sensitivity out to 700nm, they actually do, just not nearly as much.
Look up photochromatic step. It explains why >650nm works and it is well documented.

I looked up photochromatic step, but I'm not sure what I'm looking for, do you have some link to whatever you're talking about?

When I was in the Navy in 1957, I was an ECM sensor operator on a P-2 Neptune maritime patrol aircraft, originally built in 1941.  We flew 11-hour patrols low over the ocean.  At night all the pilot's Gage's and controls were illuminated with red light.  The flashlights we had were equipped with red lenses.  Most WWII aircraft were equipped the same way!   For some reason, the red light-night vision theory was obviously the belief back then.  Lieutenant Rudy Jopp, USN, Retired.

I think the most logical and simplistic scientific test in this situation would be application.  Buy red yard lamps and white yard lamps. Set up a various objects in the yard that would be increasingly harder to see in the dark (like a vision test where the letters get small but your distance is static.)
Sit outside with no light for an hour, more if you want, and then pick out the objects. This is your constant, what you will compare your results to. Repeat at least three times making note of which objects you can see.
Repeat this with each lamp, exposure for the exact amount of time as you waited in the dark. Both lamps should give you the same level of visibility, for accuracy. Take note of how long it took to be able to clearly see each object. I recommend a buddy out of your vision to keep track of time so you don't spoil the excitement by introducing light source.
Compare the results and you will know which light source affects your night-vision more.


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How do nuclear receptors locate each other to form a DNA loop?
Nuclear receptors can influence transcription far up- or downstream from their own binding sites by looping DNA (Rubina et al.; J Mol Bio 2004).
I am not sure how exactly the receptors first attach to the DNA (dimers on each site first or the whole complex on one site), but in any case they will need to attach to one response element, then loop the DNA and bind the other response element. It seems like something that should be obvious, but I cannot stop wondering: How do the receptors locate the other site?
Normally I would simply say: diffusion - it just randomly happens. But I imagine bending DNA in such a way would require a lot of energy; too much to just randomly waste it trying to find another site.

Not sure NR are actually bending a linear DNA into a loop. The loop, as Shigeta points, could already form by random coiling. Then, NR would stabilize the loop recruiting other coregulators. All together they will act like a glue.

This probably isn't the complete answer as I don't know so much about eukaryotic transcription, but maybe I can start the answer.
First of all DNA bending can be sequence dependent - the double helix is not intrinsically straight.  DNA is also pretty easy to bend - it spends most of its time coiled pretty easily around histones, and eukaryotes, supercoiled into chromatin.
In transcription though, there are proteins that come along and effect bends in the DNA or even tight loops, so that the transcription initiation complex (TIC) can be activated by transcription factors (TFs) upstream as the DNA flops over.
see this happening in this video at about :40:
http://www.youtube.com/watch?v=5MfSYnItYvg&feature=related
I think in some cases there might be other proteins bound upstream of the TIC to make the influence of various TFs greater.   I know in highly regulated genes (such as developmental genes in animals) transcription regulation can be impossibly complicated with lots if internal logic.  The classic example is ENDO16 from sea urchin (see second image) which has scores of protein binding sites in front of it.
I was told that DNA binding proteins find their binding sites at a rate faster than diffusion.  The prof told me that she thought that there might be a tendency to diffuse along the length of the DNA because of its charge.  I have no reference for this, but it might help answer your question as to how the NRs pair up so quickly.

What a funny coincidence, I once sent that video (rather, the "advanced" one) round my course colleagues when we had biochem XD Thanks for the info and references about DNA! It's unfortunate that the most important part (your last paragraph) was only word of mouth though, because that's actually what I'm wondering :/


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Percentage of genome devoted to regulating gene expression
Recently I've been studying the p53 tumor suppressor gene as a model for regulation of gene expression. It's amazing how many different post-translational modifications are known to regulate p53 activity, and how many different factors are involved in this regulation.
It is postulated that there are between 20,000 and 30,000 genes in the human genome. Is there an estimate for the percentage of these genes whose primary function is related to regulation of gene expression?

http://en.wikipedia.org/wiki/Transcription_factor

@Amy See my comment to Larry's answer.

I think you'll need to figure out a different way to phrase your question. "Gene expression" refers to transcription of open reading frames into mRNA. Post-translational protein modification is a separate cellular process and separate field of study with different terminology.

And I agree with @Shigeta - if you're getting into protein regulation and turnover, then you're pretty much just describing "life"

@Amy "Gene expression = transcription" is a very limited view of gene expression. The more widely accepted definition of expression is the derivation of a functional gene product from the gene. If the RNA itself is functional, then yes transcription is sufficient. But for protein coding genes "gene expression" definitely includes translation of the mRNA. Many proteins then require further processing to be functional, and one could argue that a protein is not fully expressed until it is functional. Whether one agrees with that or not, though, gene expression is not synonymous with transcription

@Amy Although I do agree that degradation and turnover unnecessarily broadens the scope of the question.

I'm saying that "gene expression" is separate from "protein expression." One refers to transcription and post-transcriptional modifications to RNA. The other refers to translation and post-translational modifications to proteins. And I strongly disagree with "protein is not fully expressed until it is functional" - there are plenty of genes that encode non-functional proteins. If they are translated, they are "expressed"

Okay, I'll take this out of the comments and put in an answer for all of us to work on.
To directly answer your question:

"Is there an estimate for the percentage of these genes whose primary
  function is related to regulation of gene expression?"

It depends on how you define "gene expression." And what cellular processes you want to include in that definition.
Larry's answer is the usual standard response, especially for people (such as me, ha) that have spent significant time studying transcription factors. About 1% of human genes have DNA binding domains and are thought to be directly involved in regulating the transcription of genes into mRNA - these are transcription factors (TFs). Closely related are cofactors, which regulate expression by binding to TFs or RNA polymerase machinery, but not directly to DNA.
Regulation of gene expression could also include modifications at the chromatin level - here you would include chromatin remodelers, histone acetylases, deacetylases, methylases and the histones themselves.
mRNA transcripts can also be regulated by miRNAs: post-transcriptional regulators that bind to complementary sequences on target mRNAs, which leads to translational repression or target degradation and gene silencing. So you would also include the proteins involved in this process, most notably the RNA-induced silencing complex, which includes Dicer.
There are also proteins involved in mRNA stabilization and turnover, which effects gene expression.
I'm not sure if anyone has added up all of the genes above to determine an overall percentage of the genome.
If you include in your definition of "gene regulation" post-transcriptional modification, folding chaperones, intra-cellular transport, extra-cellular and intra-cellular signaling, and so on - then Shigeta is right, you begin approaching 100%. In the most basic sense, life itself is gene regulation.

Yes, look at FANTOM and their work. There are about 2000 transcription factors and co-factors in the human genome. These are proteins, of course. If you add a couple (or few?) thousand microRNAs and a few dozen anti-sense transcripts, although small in size, you inch that percentage upwards.
With some 70% of the human genome transcribed, by some estimates, one could argue that many of these non-coding RNAs (short, long, trans-spliced) act in some way to regulate the DNA to mRNA to protein process.
(I can send you those 2000 or so FANTOM TFs if you wish. Contact me by email.)

Transcription factors are no doubt important in regulation, but my understanding was that TFs only regulate transcription. For many genes, post-translational modifications (phosphorylation by kinases, methylation by methyltransferases, etc) play an important role in regulating expression. I would like to include the genes encoding these factors in the estimate as well.

Just to be clear, by "regulation of gene expression" I meant to refer to anything that has to do with regulating transcription, regulating translation, regulating activity post-translation, and regulating degradation. Perhaps I should have worded that differently.

by these standards, the answer would be closer to 100% because any signalling protein would be involved, as well as the proteins that route signalling proteins around the various parts of the cell would be included. its hard to imagine a gene being deleted which would not affect the transcription of a gene under some conditions.  Even metabolic enzymes would probably count as transcription is often regulated by the concentration of metabolites in the cell.

@shigeta That is an excellent point. One reason I wrote the question in the first place is because I was beginning to wonder how such complex regulation schemes could be possible without the majority of genes in the genome being devoted primarily to regulation of other genes. And I understand that the question is complicated by the fact that proteins can have different functions in different contexts, which is why in the original question I used (perhaps naively) the words "primary function."

@shigeta If you were to write an answer beginning with "No, there is not an estimate" and then provide an explanation based on your comment (or even just copy and paste your comment), I'm sure you would get some up votes! You would definitely get mine, and you might even get the accepter answer!

@Larry_Parnell +1 for mentioning transcription of the majority of the genome.

it seemed too difficult to put in an answer form.  "everything is everything" is a common mindset you can slip into with cell biology and gene networks, but thanks for the suggestion.  I have no real reference.  its sort of a truism in the work.


text:
How does the strength of 3D printed tendons compare to original tendons?
There have been some attempts such as {1,2} to 3D-bioprint tendons. How does the strength of 3D-bioprinted tendons compare to original tendons? I am mostly interested in human tendons.

References:

{1} Ede, David, Nikki Davidoff, Alejandro Blitch, Niloofar Farhang, and Robby D. Bowles. "Microfluidic Flow Cell Array for Controlled Cell Deposition in Engineered Musculoskeletal Tissues." Tissue Engineering Part C: Methods 24, no. 9 (2018): 546-556. https://doi.org/10.1089/ten.tec.2018.0184
{2} Rimann, Markus, Sandra Laternser, Hansjörg Keller, Olivier Leupin, and Ursula Graf-Hausner. "3D bioprinted muscle and tendon tissues for drug development." CHIMIA International Journal for Chemistry 69, no. 1 (2015): 65-67. https://doi.org/10.2533/chimia.2015.65 (open access)


text:
Are tendons and ligaments classified under the muscular or bone system?
Are tendons and ligaments classified under the muscular system or the bone system?
Basically they are not bones or muscles and that's why I have doubt.

tendons and ligaments are classified under muscular system as they are made up of white and yellow tissue

tendons are extension of muscle connective tissue.

Tendons are intrinsically part of muscles. Ligaments are not. So for your question, we need to create a classification system which is a bit artificial, based on the tissue structure of the various components of the musculoskeletal system.

The musculoskeletal system is made up of hard and soft tissues. The hard tissue includes bones and cartilages (articular cartilages), while the soft tissues are the muscles, tendons, synovial membranes, joints capsule and ligaments. (emphasis mine)

Here is an illustration of the biceps brachii muscle (arm) from Kenhub:

It looks a little different in real life, but this clearly illustrates how tendons (the white things at the ends of the muscle) are part of the muscle. So, to answer your question, tendons are part of the muscular system (a term that I have never used as a physician. I would just say "muscles".)
Ligaments are supporting structures of fibrous tissue of nearly the same composition as tendons, but do not arise from muscle per se. (For a reason I cannot comprehend, little research is devoted to the embryonic development of ligaments.)
These are the ligaments of the elbow (and more fibrous connective tissue):

Clearly they are not bone, and they are not muscle.
If you need to artificially divide muscle vs. skeletal systems, then:
Muscle: muscle and tendons
Skeletal: bone and cartilage
"Other": ligaments, bursae, synovial fluid and membranes, etc.
The easiest thing to define is what is bone and what is not bone. Then bone may well stand alone, even without cartilage. But no one would say cartilage is part of the "muscular system".
So I hope you see that this way of separately classifying tissues which are meant to work together is artificial and perhaps misleading.

If ligaments are not part of muscle then why do we consider sacrotuberous ligament a remnant of biceps femoris ?

@JM97 We don't. The sacrotuberous ligament spans the sacrum to the ischial tuberosity and about half the time is confluent with the long head of the biceps femoris. It's not considered a remnant thereof.

https://en.m.wikipedia.org/wiki/Sacrotuberous_ligament

Some ontologies such as the FMA and Uberon draw a distinction between the skeleton and the skeletal system, with the former consisting only of bones/cartilage, and the latter including ligaments and joints. A broader concept musculoskeletal system includes muscles/tendons with skeletal system elements.
This link shows the uberon concept of 'skeletal ligament' and its placement within the skeletal system:
http://www.ebi.ac.uk/ols/ontologies/uberon/terms?iri=http%3A%2F%2Fpurl.obolibrary.org%2Fobo%2FUBERON_0008846


text:
Mechanisms of bone growth
The length of a bone is caused by growth of hyaline cartilage which is then replaced by bone tissue. How do cells know whether they should grow the hyaline cartilage? What are the key molecules that trigger the synthesis of hyaline cartilage?

How do cells know whether they should grow the hyaline cartilage?

Both growth factors and cytokines are involved but the trigger mechanism is unclear [1].
Bones grow in length at the level of epiphyseal plate where chondrocytes produce hyaline cartilage which by addition of calcium and phosphorus ions turns into hard bone [2].
It is believed that the growth process is under the regulation of local mediators like cytokines and growth factors:

In recent years, a large number of cytokines have been discovered and their molecular structures and biological activities described. A surprisingly large number of cytokines have been shown to affect skeletal tissues, at least experimentally, making this a complex topic, but one which is furthering knowledge of how the cellular events of bone growth may be so precisely regulated [3].

References

Ossification. (2014, July 3). In Wikipedia, The Free Encyclopedia. Retrieved 15:47, September 30, 2014, from http://en.wikipedia.org/w/index.php?title=Ossification&oldid=615387908
http://www.personal.psu.edu/staff/m/b/mbt102/bisci4online/bone/bone5.htm
J.S. Price, B.O. Oyajobi and R.G.G. Russell. The cell biology of bone growth. Available from http://archive.unu.edu/unupress/food2/UID06E/UID06E0U.HTM


text:
I'm 20. Can I still grow taller?
I'm 20, in about 6 months I turn 21. For some time I've been wondering whether there are natural, non-surgical and non-pharmaceutical ways that humans can continue to grow after reaching adulthood.
Please answer only if you are certain about this or you can reference any
trustworthy source.
Thank you a lot friends.

This is probably not an on topic question as it is more of a personal medical question rather than broad biological question- read the posting guidelines and try a more broad rewording of the question (about variation in growth rates with age - i.e. "when do we stop growing and how much variation is there?") other wise someone will come along and close it. But to answer your question, yes you can still grow, I'm 23 and have only recently (seemingly) stopped.

There's no normal way of getting 5cm at the age of 20. I'd say that you're more than fine, with 1.75 cm. The best thing to do is work on your posture.

Edited question to better fit Bio.SE guidelines.

Also, exercise promotes testosterone production and increased testosterone levels promotes growth - that probably partly explains my own late growth spurt (loss of asthma at 18, started sports, then grew 30cm in a year - most of which was in the first 3 months, if you want to know what growing pains feel like I am the one to ask!).

The answer is probably No.
"Long" bones - like the tibia, fibula, femur, humerus, etc. grow at the ends during childhood via a special formation called the Epiphyseal plate (also known as "growth plates"). The plates are composed of a special cartilage that grows, and slowly calcifies as a person reaches adulthood.
When the growth plates completely stop expanding is left to genetics, but generally happens 2 years after puberty finishes - about 16 for women and 18 for men. So after those ages there's little, if any, significant growth - though it can happen in very rare cases.
To date there aren't any exercises you can perform that will elongate bones. It doesn't make physiological sense; stretching puts stress on muscles and tendons - not bones. Weight lifting will compress bones, making them more dense and will make you shorter in the long run.
While there's been some success in getting chondrocytes to grow cartilage in vitro, there has yet to be significant gains in vivo, thus there aren't any medications available that would cause growth.
The only widely practiced way of gaining height after adulthood is with very painful surgery that involves a lot of braces. The bones are systematically broken, held in place, and allowed to heal. The setup looks like this:

While we get closer and closer to being able to control such things every day, for the time being (and I wouldn't count on this changing anytime soon) everybody is stuck with the height they were genetically programmed with.
As an aside: Being tall isn't all it's cracked up to be. At ~197cm I can tell you it is hell finding pants that fit.

I'd say the answer is Yes (but unlikely to be significant growth) given my own personal experience, the average may be 18 for men but there will be variance around that. A school friend stopped growing at 14, I stopped at 22.

@rg255 - Sure, there's going to be variance in everything. However, I don't want to mislead, so I use the averages. Answering 'Yes' when you're talking about 10% of the population is misleading to me.

this (http://www.cdc.gov/growthcharts/data/set1clinical/cj41c021.pdf) would certainly suggest I'm way outside of the averages - up until the age of 18 I was below the 5th percentile, now I'm above the 90th! Imagine what my growth line would look like on there. I hadn't realised there was so little variance so perhaps "no" is broadly the right answer, but there are some cases of growth right up to the age of 25 - it seems most stop about 2 years after the end of puberty which in men is marked by this event (http://en.wikipedia.org/wiki/Spermarche).


text:
Why some muscles have more tendons than others?
Very interesting examples to me are Trapezius or Latissimus - they both have places with more tendons than muscles. Taking into account that now they contract weaker and slower with all these tendons, what are the profits?

If you observe the general structure of the locomotor system, you will be able to roughly separate muscles in two main groups:

the muscles used for static work and position maintenance.
those exclusively used for manipulation of the external world.

You will also notice that most muscles with extensive tendinous attachments reside on the axial skeleton (i.e the trunk). This is because they are used for maintenance of the upright position, and examples of those are: Trapezius, Latissmus dorsi, Rectus abdominis, and many more... Given their static nature, they contain a lot of slow muscle fibers, allowing them to keep working over extended periods of time without rest. However, this does not make them weak. If the postural muscles were to have a structure similar to more peripheral muscles, for example biceps brachii, they would require an enormous number of different circular tendons extending in every direction to account for all the different body positions they act to maintain. To build a progressive example:

the biceps brachii is a fusiform muscle including two main parts. It is designed to pull hard in a limited range of movement types (i.e arm flexion). For that, it has evolved a small number of strong tendon attachments.
the serratus anterior was designed for a more extensive panel of moves. It therefore possesses several main bodies of muscles extending in different directions, with their own tendon attachment on the ribs.
the trapezius muscle has been designed to allow the head to keep its upright position (among other functions), and therefore is used as a positional link to guarantee the positional relation between head and shoulders. Its a static muscle and must be able to pull efficiently in a wide range of different directions, so its tendinous apparatus is extensive.

There are also special cases. If you take the digastric muscle of the neck for example, the tendons are used as attachments, but also as a kind of hinge to redirect the directional strength of the muscle.

I think they get weaker because they have less muscle in it. If the muscle is longer, then it has more sarcomeres and thus there is more stuff that contracts.
Could you please also add info on what benefits does this structure (large amount of tendons) give to the posture maintaining muscles?

In fact, muscle strength is in relation to its tranverse section. The more sarcomeres are pulling in parallel, the stronger.

Raoul is correct - afterall, if you exercise your biceps to increase its strength, it gets thicker, not longer. I think it would also help to add explicitly that tendons provide the mechanical attachment of muscle to bone, meaning that tendons determine at what place and in what angle the muscle's force is applied to the bone. I would expect that to be important in regards to force distribution, bone stability and energy efficiency (though correct me if I'm wrong).


text:
What is the distance between the insertion of the distal end of the bicep tendon and the head of the radius?
I was unable to find a source that could provide a measurement for the distance between the insertion of the distal end of the bicep tendon and the head of the radius.
Does anyone know a source that might be able to provide this data for the average adult human?

From {1}:

Abstract
  PURPOSE:
  There is little information in the literature describing the anatomy of the biceps tendon insertion. The purpose of this study was to map the footprint of the biceps tendon insertion on the bicipital tuberosity and to report on the relevant anatomy to assist surgeons with correct tendon orientation during surgical repair.
  METHODS:
  Fifteen fresh-frozen adult upper extremities were used in this study. The relationships between the long head of the biceps tendon, the short head of the biceps tendon, the muscle bellies, and the distal tendon orientation were examined. The length, width, and area of the biceps tendon insertion were measured.
  RESULTS:
  In all specimens examined, the biceps musculotendinous unit rotated 90 degrees externally from origin to insertion. The long head of the distal tendon was inserted onto the proximal aspect of the bicipital tuberosity, while the short head of the distal tendon was inserted onto the distal aspect of the tuberosity. The lacertus fibrosus, in all specimens, originated from the distal short head of the biceps tendon. On average, the biceps tendon insertion started 23 mm distal to the articular margin of the radial head. The average length of the biceps tendon insertion on the tuberosity was 21 mm, and the average width was 7 mm. The average total area of the biceps tendon insertion (footprint) was 108 mm(2). The average area of the long head of the biceps tendon insertion was 48 mm(2), and the average area of the short head of the biceps tendon insertion was 60 mm(2).
  CONCLUSIONS:
  Landmarks have been identified that will allow anatomic orientation of the distal biceps tendon during operative repair. The distal short head of the biceps tendon has a consistent relationship with the lacertus fibrosus and a distinct insertion on the bicipital tuberosity. The dimensions of the distal biceps tendon footprint have been determined to assist with bone tunnel or suture anchor placement during surgical repair.

(bicipital tuberosity = radial tuberosity)
Some figures from the same study:

FYI:

How correlated are the lengths of tendons in different part of a human body?
How can I measure my tendon length?

References:

{1} Athwal, George S., Scott P. Steinmann, and Damian M. Rispoli. "The distal biceps tendon: footprint and relevant clinical anatomy." The Journal of hand surgery 32, no. 8 (2007): 1225-1229. https://www.ncbi.nlm.nih.gov/pubmed/17923307 ; https://scholar.google.com/scholar?cluster=16116840451671820399&hl=en&as_sdt=0,22 ; http://www.sciencedirect.com/science/article/pii/S0363502307005163 ; http://dx.doi.org/10.1016/j.jhsa.2007.05.027 ; http://sci-hub.cc/10.1016/j.jhsa.2007.05.027


text:
Why does alcohol cause the hemolysis of RBC in a large proportion?
I had today an experiment that we put 95% alcohol to the blood which made it completely transparent so hemolysis must have occurred.
I started to think about the reasons.
I think that this is because alcohol dissolved the lipid membrane of cells outside of the cell.
Alcohol molecule is also very small.
I think that I can go through the bilayer too.
So I started to think that the other possible reason was that alcohol went inside the cell so caused

dissolution of the membrane from the inner side
increase in the volume of the cell so bursting

What are the main reasons why Alcohol cause hemolysis to the red blood cell?

Off hand I'd say your guess was a good one.  Most cells will fall apart when put into that much alcohol.  Note that biological standpoint, even 1% is too much alcohol for a human being to survive.

Well, it turns out the situation is more complex. I had assumed the answer was what rwst suggests or something to do with osmotic pressure. It seems that we don't really know that well.
In a paper from 1991, Chi and Wu suggest the following possible mechanisms :

Membrane fusion during the shedding of exovesicles might produce a transient decrease of the permeability barrier.
Increase of lipid dynamics by the alcohol could decrease the packing of the
bilayer. The membrane barrier behaves like a soft polymer, which can sieve solutes. The meshes in the polymer might become larger if its packing density is
reduced.
Lateral phase separation of lipids could induce packing defects in the lipid domain. This has been observed for long chain alcohols and postulated to be responsible for the increase of membrane permeability by amphiphiles.
Increase of the dielectric constant of the membrane by the alcohol would also increase the partition of hydrophilic solutes into the membranes. Such an increase has been postulated to be responsible for the increase of the permeability by aliphatic alcohols.
Modification of the intrinsic membrane domain might follow modification of the membrane skeleton by the alcohol. Accordingly, aggregation of intrinsic proteins might cause membrane modification mentioned under point 2 to 4.

The authors state that it is not possible to decide between the
various possibilities, but they seem to prefer point 5:

Although it is not possible to decide between the various
  possibilities from the present data, we showed that the
  release of membrane fragments from ethanol-treated RBC was not a
  requirement for the creation of membrane pores since it occurred at a
  time much later than the detection of K ÷ leakage. In addition, we
  found that changes of membane rheological properties preceded the
  permeability increase. These properties have been related to
  the membrane skeletal protein spectrin. Moreover, ethanol has
  been shown to affect the skeleton. The processes leading to
  the formation of pores in ethanol-treated RBC may thus relate to a
  deranged cytoskeletal network, followed by the aforementioned
  alteration of membrane properties.

The plot thickens, apparently, low concentrations of alcohol protect erythrocytes from hemolysis while higher concentrations can cause it. The following are extracts from Tyulina et al:

The seeming paradox between the direct haemolytic effect of ethanol on
  erythrocytes (Fig. 1) and the stabilizing effect of ethanol on
  erythrocytes undergoing NaOCl-induced haemolysis (Fig. 2) could be
  explained by the relatively small destabilizing effect of ethanol
  which is observed (<1% haemolysis) over 16 h. This effect would be
  negligible in the short time period (generally <10 min) assay for
  NaOCl-induced haemolysis where 100% of the cells are haemolysed. An
  alternative explanation for this paradox is that the mechanisms of
  haemolysis induced by ethanol and NaOCl are different.

It therefore appears that ethanol does not induce significant
  oxidative stress in the human erythrocyte, and these data are in
  agreement with previous studies (Seeman et al., 1971), in which it was
  found that low ethanol concentrations could protect erythrocytes
  against haemolysis. Although the mechanism for this protective effect
  is unknown, it has previously been suggested (Halliwell and
  Gutteridge, 1999) that ethanol can serve as a hydrogen donor in the
  elimination of the hydroxyl radical with formation of water and the
  2-hydroxyethyl radical.

The authors then state (emphasis mine):

In summary, we conclude that the damage to erythrocytes which occurs
  on in vitro exposure to ethanol may be caused, at least in part, by
  unmetabolized ethanol directly, rather than by the oxidation of
  ethanol to acetaldehyde or its conversion to FAEE.

I would guess this "direct effect" is something very much like what rwst suggested but the fact that the authors, who clearly work in this field, do not say so makes me think that the situation is more complex.
So, in conclusion, the exact details of alcohol's hemolytic properties don't seem to be understood in great detail. Admittedly, neither of these articles is very recent, if anyone can find a more up to date account I would love to read it.

REFERENCES:
Chi LM, Wu WG. Mechanism of hemolysis of red blood cell mediated by ethanol.
Biochim Biophys Acta. 1991 Feb 11;1062(1):46-50.
Tyulina OV, Prokopieva VD, Dodd RD, Hawkins JR, Clay SW, Wilson DO, Boldyrev
AA, Johnson P. In vitro effects of ethanol, acetaldehyde and fatty acid ethyl
esters on human erythrocytes. Alcohol Alcohol. 2002 Mar-Apr;37(2):179-86.
Trandum C, Westh P, Jørgensen K, Mouritsen OG. Association of ethanol with
lipid membranes containing cholesterol, sphingomyelin and ganglioside: a
titration calorimetry study. Biochim Biophys Acta. 1999 Aug 20;1420(1-2):179-88.

So the point 5 is about the proteins in the membrane that alcohol will modify.

Yes @Masi that is my understanding. But also a resulting perturbation of the cytoskeleton.

Ethanol, in less than 50% concentration, emulgates lipids and, through interference with hydrogen bonds, leads to conformational changes in proteins. Higher concentrations lead to denaturation of proteins and osmolysis of cells through small defects, so they finally burst, as ethanol forces a concentration equilibrium. This is why it's a good desinfection substance. But you could use any other small molecule polar solvent.
http://en.wikipedia.org/wiki/Ethanol#Antiseptic


text:
Is there such thing as a generic "metabolic type"?
A while ago I picked up a book called "Eat right for your metabolic type". The book discussed the effects of the endocrine system on the overall shape and the speed of metabolism.
The book outlined few major metabolic types:

Adrenal
Thyroid (hypo/hyper)
Muscular

The book proceeded to discuss the overall shape of the body, including shape of fingers to help identify the metabolic type and give suggestions on which foods to avoid for a particular type.
The book then gave examples of effects of foods on metabolic types - for example an Adrenal type who eats too much sugar would crash and compensate for this by sleeping.
Since I can no longer find that book in print, I'm interested if there's really such a thing as a metabolic type that can be easily identified ? Are there indeed some foods that people should avoid eating?

In general the answer is yes. However, the degree in which this is true and the degree in which the human body can adjust and adapt to new food types is larger misjudged. I am of the opinion that metabolism is largely controlled by the microbiome. It is largely recognized that the gut biome does adjust depending on diet and will also vary depending on drug intake. From previous meta-analyses, it has been noted that there are three subtypes of microbiomes. In a particularly famous study, it has been noted that Japanese and only Japanese people have the microbiome to digest seaweed due to the remarkable volumes of sushi that they eat.

Very interesting article!

That book was likely crap, but in short the answer is yes, probably there is a genetic basis in the metabolism, with human 'types' that could benefit from a personalized nutrition. The discipline studying these relationship is called nutrigenomics, and the main concept is similar to what is being told for personalized medicine. The bad news is that unfortunately this is not easy to identify, surely not from the form of your finger.

Not from your finger … but possibly from metagenomics.