text:
Why does inert gas asphyxiation trigger unconsciousness almost immediately?
According to an official safety bulletin from the U.S. Chemical Safety and Hazard Investigation Board:

"Breathing an oxygen deficient atmosphere can have serious and immediate effects, including unconsciousness after only one or two breaths."

Most people can hold their breath for at least 30 seconds and sometimes up to several minutes; clearly, breathing an oxygen-deficient inert gas will affect a person far sooner than simply holding one's breath.
An inert gas like nitrogen is not inherently toxic, so why does breathing a concentrated inert gas cause unconsciousness almost immediately? Does it replace the oxygen that would otherwise remain in the body while holding one's breath?

Truth: it doesn't. That's why Wikipedia is a terrible source for scientific information.

@anongoodnurse The Wikipedia article is merely quoting an official safety bulletin from the U.S. Chemical Safety and Hazard Investigation Board, which is why you should actually check the citations in an article. I even included their citation in my question.

I did check Wikipedia, and the article (it's curious why people assume commenters don't read the citations.) They do not cite a study to support the statement (not rodent studies or other; not even solid observations.) I've been reading scientific literature all of my adult life; I'm also a physician. That statement is flat out incorrect. There are substances/gasses that can kill in a few breaths, but inert gasses in normal circumstances are not as dangerous as the statement makes them appear. If they were, people would die from recreational helium use (they don't.)

One reason you can hold your breath for 30 or more seconds is that you are not denying your body oxygen during that time.  Wikipedia says:

After exhaling, adult human lungs still contain 2.5–3 L of air, their functional residual capacity or FRC. On inhalation, only about 350 mL of new, warm, moistened atmospheric air is brought in and is well mixed with the FRC. Consequently, the gas composition of the FRC changes very little during the breathing cycle.

Hence you are refreshing your lungs' air with only 10-15% fresh air with  each breath.  Furthermore, normal exhaled air has reduced the oxygen to about 16% from the 21% of fresh air.  So there is a significant amount of oxygen remaining in the lungs at the end of a normal breath.  When holding your breath, much of this remaining oxygen can also be used, albeit at a declining rate due to the reduced amount of oxygen.  Note also that when trying to hold one's breath it is typical to fill the lung with more air than usual, thus providing a greater amount of oxygen.
When breathing an inert gas instead of air, the situation is radically different. There is no period where you are receiving any level of replacement oxygen. Normally your blood has some oxygen in it at all times, even when returning through the veins to pick up more oxygen from the lungs.  However if the lungs have only inert gases in them, the remaining oxygen in the blood will be diffusing out of the blood and into inert gas in the lungs, making the lack of oxygen more severe.  This means that highly-deoxygenated blood will flow out to the body's tissues, where if there is any oxygen present it will diffuse out of the tissues into the blood.  This will quickly impact the tissues, and brain tissue has one of the highest requirements for oxygen.
The problem is not that the inert gas replaces the oxygen in the blood as such, it's just that the oxygen isn't available.  All gases diffuse between the blood and the gas in the lungs.  The inert gas nitrogen (79% of air) normally diffuses this way and is in balance between the blood and the atmosphere. Oxygen and carbon dioxide diffuse too, of course, but they are also helped along by the hemoglobin in red blood cells.  The hemoglobin grabs either carbon dioxide or oxygen, preferring the latter.  The gas molecules so grabbed had already diffused into the blood.  The lack of oxygen in the inert gases in the lungs means carbon dioxide will build up, which is a negative thing but minor compared to the lack of new oxygen for the tissues.

Great answer, thanks!

This answer is wrong.  Lung/plasma O2 % cannot be diluted to ~0% in one or two breaths (look at helium). The quote is an oft repeated one which has no scientific source (google it in quotes. You'll see it stated on a number of websites without one study to back it up.) Also, CO is not an inert gas, it is preferred by Hgb, yet death does not follow one or two breaths. Even cutting off all O2 to the brain (e.g. effective manual strangulation) is not immediate. The quote is nonsensical BS, which you've treated as fact. Note that there's no source on Wikipedia, which is always a bad sign.

As an example of inert gas inhalation, take helium. Someone on a talk show has a helium balloon. They exhale and take a breath (#1) and talk in a high voice. When done, they take a second breath (#2) and squeek on. Have you ever seen them suddenly keel over dead? No. Because it isn't true. The physics/physiology of breathing is much more complex.

@anongoodnurse The Wikipedia article does have a citation for the quote, it's currently citation #3 (which appears a few sentences later in the paragraph). The quote comes from an official safety bulletin from the U.S. Chemical Safety and Hazard Investigation Board, a federal agency.

No, the Wiki citation is for accidental deaths from nitrogen inhalation over a period of decades, not specifying "number of breaths" (i.e. it does not have a source for that statement.) Wikipedia editors often misinterpret scientific literature, which is why I think it's a terrible source for scientific information. Writers of publications sometimes make inaccurate statements, which make it into the lay press. This is one of them. For whatever reason, there's a lot of BS floating around as "facts".

@anongoodnurse You are mistaken. The quote which I used is a direct quote from an official safety bulletin from the U.S. Chemical Safety and Hazard Investigation Board, a federal agency. This is cited in the Wikipedia article and I included the citation in my question. If the quote is wrong, that's the USCSHIB's fault, not Wikipedia's fault. See page 2 of the bulletin.

@anongoodnurse And of course if an article on Wikipedia is factually incorrect, you should edit the article to correct the mistake.

@user45623 - I'm not a Wiki editor, and I don't make a habit of going around correcting all the mistakes on the internet. I don't know why you're so defensive of this incorrect statement; it's not directed against you personally. I'm an ER doc, and I have seen plenty of death, but not even one from an inert gas, which makes sense as there were only ~80 deaths from Nitrogen inhalation in the decade covered by the CSHIB. (That makes the likelihood of my seeing one pretty damn low.)

@user45623 - I am not mistaken; I know how to read. Most inert gasses aren't widely available, but Helium, Nitrogen and CO2 are, and recreational helium use is quite common. Have you ever seen a death from recreational helium use? Neither have I. Do you not think you would have heard of at least a few if the statement were true? As an ED doc, I certainly should have seen one or two in my career if the statement were true. However, it is not. You don't need to take it personally unless you made the statement yourself.

@anongoodnurse My apologies; I was not questioning your knowledge or credentials. It sounded like you were saying Wikipedia had no citation for the quote, and I was saying "yes, they have a citation, it's in that safety bulletin". As far as the accuracy of the safety bulletin, I have no opinion on the subject. My question was originally prompted by a recent news article about 6 workers dying from nitrogen exposure in a poultry facility; one source said they died instantly, but specifics are light. If you'd like to share your knowledge as an answer, please do so.

@user45623 - The way your question is framed, "It's not true" is not an acceptable answer, only why it's true. As to the citation, see the above comment to this user. I don't mind people questioning my knowledge or credentials; anyone can claim to be a physician. Common sense is my defense: the rarity of deaths attributed to "one or two breaths" of an inert gas compared to the common use of helium and nitrogen should be telling in and of itself.

@anongoodnurse When a question is framed incorrectly, just acknowledge this in your answer. If I wrote a question with some ridiculous premise like, "How come humans are immune to harmful effects of radiation?", it would be perfectly valid for you to post an answer explaining that humans are not immune to radiation but rather are vulnerable to radiation sickness, cancer, and other effects.

@user45623 - I appreciate your encouragement, but SE doesn't work that way. You answer the question asked, or you skip it. Comments are used for disagreement.

"Your question contains a flawed premise; here's why" is answering the question that was asked. It's a valid type of answer; I've seen it used by others and have used it myself.


text:
How do adenoviruses interact with muscle tissue that it makes them acceptable as vector viruses?
From what I understand certain attenuated adenoviruses are popular as a vector virus, meaning a virus that is used as the active agent in a vaccine to infect cells and trigger a helpful immune response.
Of course, this use assumes that the vector virus can indeed infect cells and cause them to replicate the target protein in the first place. From what I can tell, how adenoviruses attach to cells and their receptors is imperfectly understood and furthermore live adenoviruses seem to often prefer infecting cells in organ tissue, not muscle tissue, so what makes researchers confident that adenoviruses are effective as vector viruses when injected into a muscle?

There's research going back three decades that adenoviruses can infect muscle fibers, e.g. Quantin et al. 1992. This one in particular was conducted for the purpose of evaluating potential to treat muscle disorders, although the gene incorporated in the virus was just a reporter gene, i.e. "does nothing" besides allowing easy identification of the protein expressed.

We constructed a recombinant adenovirus containing the beta-galactosidase reporter gene under the control of muscle-specific regulatory sequences. This recombinant virus was able to direct expression of the beta-galactosidase in myotubes in vitro. We report its in vivo expression in mouse muscles up to 75 days after infection. [...]
To test whether the adenovirus construct is able to direct
beta-galactosidase expression in muscle, we injected 108 plaqueforming
units into the thigh of either newborn, 1-week-old, or
4-week-old mice. Very strong histochemical staining (>30
positive fibers) was detected in the muscle around the injection
site up to 2 weeks after infection, even in mice that were
infected at 4 weeks [...]. In the latter case, staining was
present over a distance of at least 8-9 mm, and most of the
positive fibers appeared stained over a length of 1.5-2 mm.
[...] These data were obtained by staining the
muscles as a whole. The internal fibers may not have been
accessible to the reagents because of the tight structure of the
muscle, thus leading to an underestimation of the number of
stained fibers. This was confirmed by incising some infected
muscles before staining: in addition to external fibers, some
internal fibers appeared positive.

FIG. 3. Expression of beta-galactosidase in muscle of infected mice. (A and B) Muscle of 4-week-old mice analyzed 14 days after injection. (C and D) Muscle of newborn mice analyzed 75 days after injection. (Bars = 2 mm.)

The vector used was just "run of the mill" Ad5 with E1 and E3 deleted, i.e. non-replicating.
Of the newer "stars" of vaccinology, ChAdOx1 has definitely been tested in this regard, in fact also compared with the Ad5 "gold standard":

To further investigate the difference in luciferase expression between vectors, BALB/c mice were vaccinated with HAdV-5 or ChAdOx1 vectors expressing luciferase and muscle tissue samples from the site of injection and draining popliteal lymph nodes were harvested 24 h post vaccination. Luciferase expression was detected ex vivo in both muscle and lymph node tissue of vaccinated animals (Fig. 2A,B). Since the extraction procedure differed between muscle and lymph node samples, absolute luminescence units cannot be compared between tissues. However, in lymph node samples, mean luminescence activity after HAdV-5 vaccination was approximately 20-fold higher than after ChAdOx1 vaccination (Fig. 2A). By contrast, mean luminescence activity within muscle samples was less than 3-fold greater after HAdV-5 vaccination (Fig. 2B). These data suggest that the greatest differences in transduction efficiency between HAdV-5 and ChAdOx1 in vivo occur within the draining lymph nodes after intramuscular vaccination.

Given this, I strongly suspect Ad26 was tested in this regard as well, but I can't be bothered to search for that paper.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


text:
How does blood reach skin cells and other closely packed cells?
When I see diagrams of cellular structures such as the layers of the skin, these diagrams show the cells as being closely packed together. For example here is a typical such diagram:

So, it shows the capillaries of the vascular system going only to the bottom of the many layers of tightly packed cells. So, I assume that all the cells need oxygen, so they all need to be in contact with the blood cells that bear oxygen, so how does this happen? Obviously each individual cell can't have its own personal capillary. If blood were to be released just loosely around the cells that would not work either because the blood would have no way to get back. All the blood has to be in vessels of some kind so it can circulate. But these vessels are not shown as reaching the upper skin cells in any way, so how are those cells getting oxygen?

Would you be interested in "plasma" defined as blood minus erythrocytes, and plasma being pulsed around cells as "interstitial fluid", then reabsorbed into blood stream? This interests me, and I'd be willing to elaborate in some answer.

The skin is highly vascularized up to the epidermis, with dense vessels right at the top of the dermis (your picture omits these, but you will find them in better diagrams like this one). The epidermis itself gets substantial oxygenation from the outside air (see Stücker et al, for example), though the very outermost layers are not metabolically active ("dead") and do not require oxygen.
As a gas, oxygen moves quite well through tissue, and cells can get sufficient oxygen from sources up to a few hundred micrometers away. No need to be in direct contact with blood cells (and typically no tissues of the body are in direct contact, besides vascular endothelial cells that line all blood vessels). Many small animals have no need for a circulatory system because their entire body is close enough to the outside for gas diffusion.

Stücker, M., Struk, A., Altmeyer, P., Herde, M., Baumgärtl, H., & Lübbers, D. W. (2002). The cutaneous uptake of atmospheric oxygen contributes significantly to the oxygen supply of human dermis and epidermis. The Journal of physiology, 538(3), 985-994.

What is the largest "small animal" which doesn't have a need for a circulatory system?  (Approximately, to an order of magnitude, I'm just trying to get a feel for how much depth you're talking about.)

@davidbak Flatworms and roundworms are probably a good place to start. Some of these can be quite large (some flatworms can be meters long) but in that case they are also quite thin. Jellyfish, too, can be quite large but their bodies are also quite thin despite the space they take up; they also don't have a lot of metabolic need.

It's also worth noting that the ~15-60 most superficial layers of keratinocytes (epidermal epithelial cells) are not metabolically active (i.e., "dead") and therefore do not need to receive nutrients/gasses or eliminate wastes. Therefore, exchange with blood is not needed beyond 10-15 layers of "living" epithelial cells in the deeper epidermal strata.

The deeper, active strata are approximately 20-100 μm thick 1, which is within the "few hundred" μm range for interstitial gas exchange that @BryanKrause mentions in his answer.

See here and here for more info.

 Modified From: wikimedia

Citations:
 1. Olatunji, O. and D.B. Das. 2011. "5.48 - Drug Delivery Using Microneedles." Pages 625-642  in Moo-Young, M., editor. Comprehensive Biotechnology (Second Edition), Academic Press, ISBN 9780080885049.

Ok, so you are saying that the oxygen just diffuses out of the hemocytes through multiple layers of cells? What about nutrients, can nutrients diffuse the same way? I guess my question applies to muscle as well as skin. Like when I eat say a chicken breast, I don't see any blood vessels in the chicken breast.

@ImprisonedRhesus My post is really more of an extension of BryanKrause's answer and is only meant to point out the anatomy of the skin (i.e., that superficial layers aren't alive). I wasn't gong to extend my post with further physiology (e.g., interstitial exchange and transport) due to current personal time constraints. I hope someone else can provide you an adequate response in a separate answer

@ImprisonedRhesus Also, I would keep your question focused on skin here. If you're interested in muscles or tissues more generally, it might be worth taking what you've learned here and asking another question that builds from this one.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


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Can someone explain DNA methylation reprogramming in simple terms to me?
From what I understand, one of the challenges of cloning is that the DNA methylation that is supposed to occur during embryonic development does not occur normally and this prevents natural gene expression in the cloned zygote. However, the typical descriptions of these processes are highly technical and beyond my monkey-level intelligence. I was wondering if someone could explain in simple terms why DNA methylation does not occur normally in naive cloning processes.

Your description sounds a bit confused. Perhaps the best way to think about it is that a natural zygote's DNA has undergone epigenetic "programming" that places different genes in different expression states appropriate for that stage of development (for example, you wouldn't want to turn the cell into a cartilage cell at that point, so those genes should be off). DNA methylation is one method of such programming, there are others known, and likely additional unknown ones as well.
If you replace the nucleus of a zygote with a non-zygote nucleus, much of the programming won't be appropriate for the zygotic stage and development won't proceed properly.  Cloning technology involves developing processes and reagents to reprogram the nucleus into a state that is compatible with normal development once it is inserted into a zygote.


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How much oxygen is released by Hemoglobin per 100ml blood
Question

Red blood cells carry oxygen from lungs to the whole body. The percent saturation of hemoglobin
with oxygen depends on the partial pressure of oxygen. Higher partial pressure of oxygen means more
hemoglobin can carry more oxygen, while lower partial pressure of oxygen means hemoglobin releases
oxygen. The relationship is shown in the graph.
Partial pressure of oxygen
In lungs = $\ce{11 kPa}$, in muscles = $\ce{2 kPa}$
100% oxygen saturated hemoglobin carries:
$\ce{20 mL oxygen/100 mL blood}$.
While going to muscles from lungs, what is the amount of oxygen (in mL) released by hemoglobin per
$\pu{100 mL}$ blood? Write it as an integer.

My progress
So, it seemed like too easy question to me.
As the graph says, Saturation of Hemoglobin with Oxygen is 100% when partial pressure of oxygen is $\pu{14 kPa}$ So, at $\pu{14 kPa}$ it carries $\ce{20 mL oxygen/100 mL blood}$
With this information, it can be said that at $\pu{11 kPa}$ and $\pu{2 kPa}$ it will carry $\pu{15.71 ml}$ and $\pu{2.85 ml}$ respectively.
Which are actually the amount of oxygen carried in lungs and muscles. So, while going to muscles from lungs, it should release
$\ce{15.71 - 2.85 = 12.86 ≈ 13 ml}$
So, $\pu{13 ml/ 100ml of blood}$
But I have confusion if this is correct reading this part

Higher partial pressure of oxygen means more
hemoglobin can carry more oxygen, while lower partial pressure of oxygen means hemoglobin releases
oxygen.

I am confused, if the way I found the difference is proper
So, I am not sure if that was the correct way. Is it the correct procedure ?

If you can solve this problem, why are you posting here? Don't you have an instructor to mark your work? This is a biology question and answer site, not a homework checking site.

I’m voting to close this question because the question appears to be an attempt to use the site as a homework checking service.

I don't have any tutor to check and I am practicing a olympiad questions which answers are never given. People here ask for efforts to add so I added how I progressed. But when I have done this, people are closing it. How funny

Your calculations are wrong and you don't seem to be using the values from the graph. For example, the graph does not show the hemoglobin 100% saturated at 14 kPa.

I think this question demonstrates the sort of effort required under our homework policy; they've shown their work towards an answer. I am also, however, a bit concerned with this site being used as an "answer checker" service when answers are not provided, even if work is shown. Questions should be asked in ways that are useful to others.

@Armand, I noticed it just now. But all I am concerned about is the process. Thanks though

I'd solve differently, in a way that removes some imprecision in your estimates and incorrect assumptions.
We care about two points on the graph: saturation at 11 and 2 kPa. At 11 it reads approximately 96% saturated; at 2 it reads about 22% saturated. So we can say the difference from 11 kPa to 2 kPa is 74% of the total capacity of hemoglobin.
If we know the total capacity is 20 mL/100 mL; then 74% of 20 mL is 14.8 mL. As an integer approximation I'd write 15 mL.
You shouldn't be caring or using the 14 kPa number at all, it's completely irrelevant. As Armand points out, hemoglobin is not 100% saturated at 14 kPa. More importantly, the graph shows that the relationship between pressure and oxygen saturation is not linear. It seems like you've done your math by assuming 14 kPa is maximal and then there is a linear relationship so that at 7 kPa it is 7/14=half, at 2 kPa it's 2/14, etc. You could plot these assumptions out on the graph and you'll find it doesn't look like what is shown at all. It turns out to be not a completely terrible approximation, since your answer of 13 mL is fairly close to 15 mL, but it's not precise enough to get to the nearest integer.

Thanks for pointing out my problems. I never noticed those errors in my assumption. Thanks a lot


text:
Why would this viral strain-specific antiserum fail to immunoprecipitate the same (98% identical protein) from another strain?
I'm reading this paper https://www.ncbi.nlm.nih.gov/pmc/articles/PMC392475/  and I can't work out why a certain immune serum didn't work on the same viral protein but from different strains.
The serum was extracted from tumour-carrying animals infected with the 'SR' strain of Rous sarcoma virus and was later used to immunoprecipitate out the viral protein p60-src from virusinfected cells. The cells in question had been infected either with SR or other closely-related strains, all strains express the same protein. But the antiserum only extracted the SR strain's p60-src and not the same protein from other strains. I thought it could be because the serum had by chance targeted an epitope specific to the SR strain, so you get a lot of proliferation of B cells complimentary to this epitope, therefore overshadowing the detection of other epitopes. But 1. I think the serum was taken from multiple rabbits and surely they wouldn't all have happened to do this. and 2. a later paper I read said that p60-src is 98% the same across SR, Pr, Br strain etc so it seems unlikely to have latched onto an SR-specific bit. And yet, the authors state that due to similarities between SRC genes, "... similar gene products are probably present in cells transformed by other strains of ASV, but they are not detected because of a lack of crossreaction with the currently available antisera."
So my question is, what is causing this lack of crossreaction? Apologies if the answer is very obvious, I am new to the subject and have very little knowledge of experimental methods currently. Thank you in advance for any insights, or corrections on the conclusions I've drawn so far as they might be inaccurate too.
Note: thanks mods for letting me edit the question to improve privacy.

Please don't delete upvoted questions with an accepted answer. If there is a fundamental problem with the post, please flag the question for mod attention, or post a question on it in meta. Thanks.

If you have concerns about plagiarism software please use the edit function in a meaningful way to change the question.

As you note, the viral strains are not identical; it's unclear from your question the actual amount and position of amino-acid differences among them, but it's not surprising that even a portion of the protein would have an immunodominant epitope and thus drive reproducible strain-specificity of any immune serum produced.
Remember that the rabbits or other animals used to produce antibodies are typically at least somewhat inbred strains raised for lab use and so are likely to have less genetic diversity among individuals than you might otherwise expect.
Another paper from this time period reports that different immune sera generated from related virus strains and produced in different animals ranged from immunoprecipitating the src viral protein in zero of the viral strains tested up to immunoprecipitating the protein in all viral strains tested: "Detection of the Viral Sarcoma Gene Product in Cells Infected with Various Strains of Avian Sarcoma Virus ..." Brugge et al (1979) Journal of Virology Vol 29 No 3 p 1196-1203

They may be; they also might not be. I would think that in general you would expect to see less variability in the immune response (not necessarily in the range of targets) among lab animals.  However naturally-generated immune sera are quite complex and need to be individually characterized once they are generated. Also remember that the paper you are reading is from 40+ years ago, before PCR, before easy DNA sequencing, before most bio-informatics, before most understanding of oncogenes, etc.


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What is the minimum light intensity that a human eye can detect?
By doing a quick search in Google, I find a series of pages dedicated to physics exercises claiming that the human eye threshold for light intensity is $10^{-10}$ W/m${}^2$. However I cannot find any reference for such a value. Is it even the right unit to use here? Considering the existence of the luminosity function and the difference between W, lumen and cd.
I am interested in the minimum light intensity (in W/m${}^2$ if possible) an average human eye can detect in the lowest part of the visible spectrum (red).

I would have thought the answer would contain a time component as well. (Although if it really is "the eye can detect as little as 1 photon" perhaps not).

@SoronelHaetir The watts should account for the time component, since power is energy over time.

@SoronelHaetir some papers, listed below, claim to detect a single photon.

@SoronelHaetir Actually, for 1 photon the time component is very important: specifically, detecting just 1 photon requires that there be effectively zero photons from the outside ahead of time to detect it as a 'flash'/'something happened'. Nervous systems and brains in general are difference detectors.

From Hecht, S., Shlaer, S., & Pirenne, M. H. (1942). Energy, quanta, and vision. The Journal of general physiology, 25(6), 819-840.:

Direct measurements of the minimum energy required for threshold vision
under optimal physiological conditions yield values between 2.1 and 5.7 X
10-10 ergs at the cornea, which correspond to between 54 and 148 quanta of
blue-green light

and

in order to produce a visual effect, one quantum must be
absorbed by each of 5 to 14 rods in the retina

They're talking about blue-green light, which rods are most sensitive to. I agree with you that light intensity in units of power density doesn't seem quite right, I'd think about it in terms of counting photons instead. Basically they estimated you need somewhere around 10 photons absorbed, with about 1/10 photons being detected. A more recent paper suggests humans can detect as little as a single photon:
Tinsley, J. N., Molodtsov, M. I., Prevedel, R., Wartmann, D., Espigulé-Pons, J., Lauwers, M., & Vaziri, A. (2016). Direct detection of a single photon by humans. Nature communications, 7(1), 1-9.
As far as "red", it'll depend how "red" you go. Rods aren't particularly sensitive to deep red light (I see quite a range of estimates depending on experimental conditions, but e.g. Lamb, T. D. (1995). Photoreceptor spectral sensitivities: common shape in the long-wavelength region. Vision research, 35(22), 3083-3091. shows about 4 to 510 less sensitivity of human rods at 700 nm compared to peak), and cones are far less sensitive to light because they require multiple photon hits on a single cone to detect; they're also sparse in the periphery. See for example:
Donner, K. (1992). Noise and the absolute thresholds of cone and rod vision. Vision research, 32(5), 853-866.
As such, when people are interested in the thresholds of human vision, they're not usually looking in the red spectrum.

Thanks for the sources, I will check them out. I was interested in red because of the definition of the Draper point. I was wondering if it could be predicted more exactly by knowing the human eye threshold in the longwavelenght red.

@Mauricio Got it; I really wouldn't recommend using human perception for approximating physical quantities. For one, human perception is extremely influenced by conditions. These sensitivity values are effectively in perfectly dark conditions (though the Hecht paper I reference had participants focus on a dim red light and then presented the flash stimulus on the periphery; the dim red light was needed to keep the subjects eyes still).

If you're looking at Draper you're not only looking at just the edge of the light emitted which is mostly in infrared, but you're also looking at a measure that's basically a dude in a room looking at a rock - 1800s science-worthy, perhaps, but not really modern-day.

A single photon...?? That's really "out there" yet it's what the publication is claiming. Remarkable, despite requiring a bunch of special conditions. Would be nice to see an SE-like summary of that paper, I didn't dig into it.

@OverLordGoldDragon It's probably better to characterize their result as a "single photo-isomerization", which is caused by a single photon. And this is not something noticed every time, mind you, it's that an observer can detect it (barely) above chance (about 52%). https://en.wikipedia.org/wiki/Stochastic_resonance_(sensory_neurobiology) likely applies. It's really not appreciably different from the Hecht result besides their technique.

Apparently that value is coming from a study by Clarke & Denton in 1962 where it is extensively cited in book1 about sound scattering in ocean.

The threshold intensity which the human eye can detect a small source of light is indicated as about 10-10 µW/cm2 (Clarke & Denton, 1962)

Beside the threshold has also been measured in terms of flux2.

The threshold for a steady, effectively point, source of light presented against a
zero intensity background, which represents the smallest energy flux detectable
by the human eye, has apparently not been recently determined. Walsh (1953)
gives a value of 750 quanta/sec entering the eye.

References

International Symposium on Biological Sound Scattering in the Ocean, Airlie House, G. Brooke Farquhar, U.S. Government Printing Office, 1970
THE MINIMUM FLUX OF ENERGY DETECTABLE BY THE HUMAN EYE, F. H. C. MARRIOTT,VALERIE B. MORRIS AND M. H. PIRENNE, J. Physiol. (1959) 145, 369-373 (PDF)
https://www.olympus-lifescience.com/en/microscope-resource/primer/lightandcolor/humanvisionintro/
https://sites.ecse.rpi.edu/~schubert/Light-Emitting-Diodes-dot-org/Sample-Chapter.pdf
https://people.cs.umass.edu/~elm/Teaching/ppt/691a/CV%20UNIT%20Light/691A_UNIT_Light_1.ppt.pdf
Light Detection and Sensitivity by Vasudevan Lakshminarayanan,
Handbook of Visual Display Technology, 2012, ISBN : 978-3-540-79566-7 (link)

It should be noted that $10^{-10}~\mathrm{\mu W/cm^2}$ is 100 times less than the value given by the OP, since $10^{-10}~\mathrm{\mu W/cm^2}$ = $10^{-12}~\mathrm{W/m^2}$.


text:
Is there any relation between phyllotaxis and the Fibonacci sequence?
I had to modify the question to get into a clearer answer. I originally asked this:
Original question
Watching some TV series, I saw the claim that all flowers have a number of petals that is related to the Fibonacci sequence (1,2,3,5,8,13,....). I was wondering if this is always true and if so, why? I guess some flowers have defects, this has to be some kind of probabilistic law.
I found some websites with examples, [1]. The usual explanation claims that is an optimal packing and is somehow related to petals forming a spiral.
Looking a bit deeper, I found that to avoid petals growing in the same positions, the petals can arrange in such a way that the angle between each petals is the circumference $2\pi$ divided by an irrational number $r$ in order to cover the circle densely. The golden mean $\phi=(1+\sqrt{5})/2$ is irrational and is related to Fibonacci sequence. However, even if $\phi$  is irrational, that does not explain why would $r$ be proportional to $\phi$ in order to create the spiral, wouldn't any irrational number work?
Could anybody provide additional understanding on why the golden mean is so important here and if possible what is the biological origin of these sequences?
More insight
Some comments below were arguing that there are some clear exceptions to this rule. One answer even showed a list of flowers categorized by different number of petals (1,2,3,4,5,6,7...) which shows some violations to the rule. Others provided additional sources that claim slightly different observations but I cannot see which are right and which aren't.
Most websites agree that daisies and sunflowers inner small petals (or disc flowers) produce Fibonacci spirals. Do the external petals (or ray flowers) also count? Other links add more on phyllotaxis (the number of arrangements of petals/leafs in a plant) and consider spirals in pinecones and pineapples. Maybe it is only related to spiral patterns in plants?
I am still concerned to understanding if there is any common mechanism and why the golden ratio is important here.
In this page of UC Santa Barbara, it says that the angle is about 137.5 degrees which is equivalent to the complement of $2\pi/\phi$ or equivalently to $2\pi/\phi^2$ due to the properties of $\phi$. In this paper introduction Phyllotaxis: is the golden angle optimal for light capture? it is claimed that two other angles work too (including the Luca angle). Note that that makes the question harder to falsify, as for example the Luca sequence also includes additional numbers like 4 and 7, but I guess the important thing is some kind of ratio and not the total number of petals/flowers in a given flower/plant.
So a better question is, when and how is phyllotaxis related to the Fibonacci sequence?

Comments are not for extended discussion; this conversation has been moved to chat.

The claim that "all flowers have a number of petals that is related to the Fibonacci sequence" is simply false. Many flowers have other numbers of petals.
Consider, for example, dogwoods, which have a very clear four-petal form.  Lots of other flowers have four or six. A nice catalog of some common examples can be found on this "Ontario wildflowers" site, which lists by petal count.

The claim is still somewhat true for a certain subset of flowers as discussed in the comments above.

@Mauricio I think it's on you to show that it's actually interesting, though, or drill down to a better description of "when it's true". Birthdays follow the Fibonacci, too, as long as you exclude everyone that doesn't fit the pattern.

@Mauricio - Are you saying there are no falsehoods on the internet? Dead. Horse.

Thank you for that wildflowers site. Many years ago, I traveled the country photographing wildflowers. It brought back many happy memories.

What claim are you claiming to be "simply false"? That there is a relationship between phyllotaxis and the Fibonacci sequence? Surely not? This paper for example, states "besides the daisy head, other common examples of Fibonacci phyllotaxis—plant growth on Fibonacci spirals—include the arrangement of the sunflower's seeds, the pine cone, the petal sequence in a rose or a lotus, the sequence of leaves on a thistle, the fruit partitions of a pineapple, and the succession of twigs branching from the stem of a pear tree. T

The claim that is false is: "all flowers have a number of petals that is related to the Fibonacci sequence."  Given how much the question has changed, I have edited the answer to make it clear what I am addressing.

IMO that is trivially obvious. But this site (to pick yet another example) lists quite a few that apparently do (and that fact seems to have fascinated a  lot of people)

I will always admit when I am wrong, and I never argue this much when I am unsure of the facts. I grow flowers, have studied flowers, have photographed flowers, I know flowers. My objection is to the petals claim. It cannot be substantiated. Again, have you looked at the images of daisies I linked to? How do you explain it? By assuming I'm wrong? Yes, there is another possibility, but it's not that I am wrong.

I think this argument is not really going to go anywhere. The general claim is obviously false. jakebeal's answer is simple and clear. It may be worth looking at the extent to which specific flowers or parts of flowers follow Fibonacci sequences, but if we're going to do that we need to start with a specific question with a narrow claim about what is supposedly following this pattern, not "flowers", or this turns into a numerology game rather than science.


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What kind of insect appears in this photo?
For months my wife has been commenting about a white substance spontaneously appearing on black clothes. Under magnification, the substance appears to possibly be eggs. As you can see, the image shows a structure smaller than 0,1mm on her jeans fabric.

My clothes are unaffected. We live in Neugraben, a south-west suburb of Hamburg. We do not have any pets.

You'd be surprised how often it happens that people forget to post an image of what they're referring to.  When you add yours, could you also fill us in with a few details about where in the world are you - which country and if you're in the city, the suburbs, the countryside for visits. Do you have any pets or pests around the house/loft/walls?

Friendly note on English time expressions of this type, which are one of the top three traps for non-native speakers in my experience (in an international science laboratory). "Seit zwei Monate", "depuis deux moins", "da due mese" translate into English with the pronoun "for" — never "since". (And generally with a past tense, here a past continuous "has been complaining".)

#1: I am living in Neugraben, a south-west suburb of Hamburg. We do not have any pets.

looks like a ball of lint to me.

I think these could be the eggs of woolly aphids(Eriosma lanigerum), which overwinter and spend their winter as either nymph or egg , woolly aphids usually lay their eggs in autumn .They are mostly attached to the stem of young plants and some species on Apple trees also and their size is about 0.3mm to 0.6mm (of eggs).
These are not harmful or poisonous to humans and not so for trees but species are like Eriosma americanum "Eriosoma lanigerum - Wikipedia" https://en.m.wikipedia.org/wiki/Eriosoma_lanigerum


text:
Asexual reproduction by secondary mycelium in basidiomycetes
I'm studying in class 11 and the the following line was mentioned in my textbook: "Dikaryophase or secondary mycelium may multiply by different types of spores - chlamydospores aecidiospores, uredospores, teleutospores." My teacher told me that in secondary mycelium, karyogamy takes place and 4 basidiospores are formed by meiosis. Where does aecideospores, uredospores etc, come into the picture?

Those spores are produced by different groups. E.g uredospores by Rusts; which have two dikaryotic spores. There are different sorts of spores produced even by the one species at different times.

It’s really complex.

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer.


text:
What is this water animal in my swimming pool?
I have had a swimming pool (which is salt) for few months. 2 weeks ago I saw this:

I made a quick gif of a video:

Today, I found 4 more of this animal:

All of them that are living I found in the water. I saw one beside, but it was dead.
I'm currently in France (in the middle). Around the swimming pool there is nothing except grass for 5m. Else it's my house, a hedge or just the grass continuing.
What is it? Is that dangerous/bad news that I have some of them?

Note* Saltwater won't do them a lot of good in the long-term as they're adapted to freshwater.

That's a good point, I don't really want them in my swimming pool ...

Welcome to Biology.SE. Species-identification questions should use that tag. Amphibian is used for a group of vertebrates — these are insects so I replaced that tag with entomology. Please [edit] in an approximate size for your new "friends" as this may help with the identification. ——— Also note that whether this is "bad" is a matter of opinion, which is not appropriate for this site. Based on the suggested id (which seems correct to me) you can do some research and decide for yourself if this how you feel about their presence!

Thanks ! Yes, I search for the species-identification tag but i didn't find it. Thanks for edit. Yes, I say something opinion-based, but it's tolerated in comments ?

Corixidae (Water-boatmen).
Aquatic insect comprising 6 subfamilies and 55 genera. (The Wikipedia page's right-hand panel contradicts the detail below that).
Size 2 - 15 mm long (0.1 - 0.6 inches), six legs, the front pair are hairy and shaped like oars. Feeding on aquatic plants and algae they range worldwide except Antarctica.
If I couldn't guess from the picture which of the 55 genera it might be as so many are wide-ranging and have similar morphology.
Edit: in response to bob1's comment, the related family notonectidae (backswimmer) deserves a mention.
Being of the same order as the corixidae above (the neomorpha), the backswimmer is distinguished by ... swimming on it's back. They're slightly bigger on the whole than their cousins and although primarily aquatic are able to migrate through flight. They can inflict a painful bite and are able to pierce with their proboscis - which they use to great effect in hunting tadpoles and small fish.

Thanks, yes it's seems to correspond ! Do you know if it's dangerous ? It seems no but idk

@Elikill58 they are not dangerous but some of them can bite you,it gives a stinging sensation but it only last a very short time.

Thanks that's perfect ! :)

Good answer. You should also include the Notonectidae (back swimmers) which are very similar, and the ones that bite as they are carnivorous. The Corixidae are mostly herbivorous I think.

@bob1 Sure thing, I can't really tell from the picture which way up the thing is. Will edit.


text:
Kansas Insect (Black Bee/Wasp?) Identification
I live in Kansas (Pottawatomie County), and I found a bee-like insect in my bedroom. The creature looked like this:

The insect about 5 cm long in size (as you can compare it with the window blind), and it appeared once in the morning (9 AM) and once in the evening (8 PM). It seems to be dark in body color, with some yellowish color on its legs and wings.
Could you please tell me what is the name of this bee-like species? And is this thing toxic / dangerous to human?
In addition, what would be the best way to kill it? Do spiders prey on it? Does ultraviolet (UV-A) light attract this insect so that I can kill it with a bug zapper? Or should I call the pest control for help? Edit: Or do I have to kill it at all?
Thank you so much for your help!

@anongoodnurse Thank you so much for the help! So would it be safe to say that these wasps' sting is unlikely to cause life-threatening symptoms?

@anongoodnurse Hello, thanks for helping the OP. Do you think you could make your comment an answer? As you know, it's not ideal to have answers in comments.

@BryanKrause - Sure, sorry!

It's a paper wasp; it looks like maybe a Northern Paper Wasp (better photo needed.)

Northern Paper Wasps are most commonly found in the Midwest states. They are likely to build nests near humans as that is where a lot of wood can be found (homes, barns, sheds, fences, firewood, landscaping, etc.). The wasps use wood to create their nest.

They are 15mm to 21mm (0.59" to 0.82") long, which fits your photograph. They are considered beneficial to keeping caterpillars under check:

Northern Paper Wasps are so effective at this pest control that they are almost welcome in organic gardens since their presence negates the need for chemical pesticides.

...is this thing toxic / dangerous to human?

It stings, the sting can be painful and may cause localized swelling, but they aren't likely to sting unless you irritate it (e.g. try to kill it and miss, etc.) If you're allergic to hymenoptera stings, leave it alone and get someone else take care of it! If there are children in the house, it is probably better to kill it than to risk their getting stung.
If it appears daily, there is probably a nest somewhere in your house (a wall or attic) with a small space where the wasp can access your interior. The larger the nest, the more easily wasps get irritated, so if you ever see two wasps in your house at the same time, call an exterminator with experience in wasp nest destruction. If it were a bee, you would call a nest extractor, who could relocate the hive.


text:
Why do veins contain lower concentration of proteins as compared to arteries?

In Q 9.b, it is said that the blood in Y has lower concentration of proteins/amino acids as compared to the blood in X.
But why is it so?
The blood in Y should have more protein as the tissues may secrete some proteins into the blood as they flow like they would in case of lymph going through lymphatic vessels.

Well, that's sort of the issue, the tissue in the image isn't specified - is it gut, lung, liver, kidney? It's impossible to generalize a conclusion as we're not homogeneous colony organisms. Can you add detail at all about the specifics of the question?

The tissue isn't specified in the question

Well, I guess that's the answer then, "They don't, unless they do."

"In this image it is said that the blood in Y has lower concentration of proteins/amino acids as compared to the blood in X." - the image doesn't say this to me at all, is this a quote from someplace? What's the actual statement? I don't see how anyone can begin to approach a "why" without first clarifying what's being explained. Where did you encounter this image? Who is telling you about X and Y and what precisely do they say? Is it even intended to be true or just a prelude to asking some other question?

lower concentration of proteins/amino acids/fatty acids/other named nutrient

This answer key wants to allow an answer that the blood at Y has fewer nutrients than the blood at X because you should assume that some respiring tissue is taking up nutrients from the blood supply.
In my view, "proteins" does not fit on this list. Protein is not a "nutrient" at the cellular level. For some reason, the person who made this answer key included protein in the allowable list. Your question should not be "Why do veins contain lower concentration of proteins" but rather "Why does this answer key allow for 'protein' as a possible answer". Maybe they don't want to make a distinction between protein and amino acids for some reason; I disagree with them, but that's okay. Maybe some student made a good argument for protein in some specific tissue and they simply decided to include it in the answer key as close enough.
I would very very strongly advise against using an answer key as a way to study a topic, only to judge your potential answers to that question. Read the text that goes along with it, where the author has made a more intentional approach to the content. Reading the answer key is not a good shortcut.


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Does the red blood cell in frogs undergo amitosis?
It is a notion particularly popular among Chinese high school Biology textbooks, that the red blood cells in frogs can undergo amitosis (not mitosis), a claim which I have not been able to find reference. A search on Pubmed led me to this article, which states:

The nucleus of the frog erythrocyte is not a regular ellipsoid; ... a single nuclear invagination located at one end of the long axis is frequently seen in the phase microscope.

However I have also been unable to find more recent researches on the nature of this observation, and whether it is related to amitosis. Can you help me find some?

"Circulating" Red Blood cells are terminally differentiated cells, and cannot divide further. What appears to be the notion is that ejection of nuclear content is biased to one daughter cell (which is then eaten up by macrophages), and some researchers have dubbed it as amitotic process, instead of defining it as a maturation process. In case of humans the process of losing the nucleus from erythroblasts occurs prior to entry in circulation (in adults). You can read this if interested.
However, exceptions do exist... in newborns (and even in foetuses) nucleated red blood cells can be seen in circulation (although the count maybe low). In foetuses, this count is usually high when the oxygen demand increases (hypoxic/acidemia conditions). Read here.
The process from normoblasts to reticulocytes and finally RBCs is one of the setting points in evolution. In frogs (or amphibians in general), and other lower vertebrates (like fish, reptiles etc.) the presence of nucleated blood cells just identifies them as less advanced on the evolutionary-tree. Since higher order vertebrates have smaller blood vessels and complex respiratory organisation, evolution decided to squeeze out the nuclei from these cells to allow easy passage even via micron-thin vessels without compromising oxygen transport.
In short, the presence of nuclei doesn't necessarily determine the mitotic capability. RBCs have long been considered as terminally differentiated cells, and do not divide. If there are any studies reporting "circulating" RBCs as (a)mitotically active, I am unaware of it.

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text:
Bodyweight loss vs calorie shortfall
I have read that 1g of pure fat has 9 Calories.
If I dieted successfully in a way that did not cause me to loose muscle, and I had a cumulative calorie shortfall of 90,000 calories. Would that correspond to a reduction of bodyweight of 10kg? Or would it actually be a bit more, because presumably each kg of fat in the body is tied to a certain amount of water packaged with it?... and if so, how much more than 10kg?

Great question and this is something that is commonly misunderstood – as you lose weight (i.e. Fat mass) your body will compensate metabolically to conserve energy and lower your resting metabolic rate. It's commonly stated that a pound of fat is about 4000-4500 calories which technically is true (with a bomb calorimeter), but you can't just try to burn and extra 4500 cal a day - it doesn't work that way – the body is much more complex metabolically

You hit upon several ideas in your post.  First, you are absolutely correct that body fat is composed both of lipids and water, so a 10kg weight loss does not correspond to 90,000 kcals.  The most commonly accepted figure is 7700 kcals per kg of body fat lost (Hall, 2008), but this is a rule of thumb at best.
The translation from caloric deficit to body fat loss is fairly complex, and is the result of feedbacks between metabolism, weight, and other responses.  The National Institutes of Health researchers built a fairly intricate model estimating the actual responses as a differential equation (simulation and references available here), which would probably be a good place to start.
If you're inquiring not from general curiosity but with an interest in developing your own nutritional plan, keep in mind that nutrition is a lot more than merely calories.  It is critical to get macro and micro nutrients, of course, but other factors such as dietary fiber play an important role in the health outcomes.

that answer doesn't really address the question of how the body adjusts metabolic rate with changes in weight loss and lean/fat mass - that calculator from NIDDK is for calculating a weight loss plan - it doesn't address the physiological adaptations to weight loss - i think that's what Mick was asking about in the question (?)

I don't know whether their public front end actually does account for it, but I believe their model does.

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text:
Which process is right to describe V(D)J recombination? RAG-1 and RSS recurring process
I'm studying V(D)J recombination. I think I have two incompatible books about explantaion of the process. Which is right?

In Molecular Biology of the Cell 5th Ed., firstly RAG (-1?) combines to RSSs of V and J genes independently. After that, a hairpin loop is formated by paring random(?) RAGs.
In Janeway's Immunobiology 8th Ed., RAG complex (RAG-1 and RAG-2) has two sites for RSSs from the beginning. And in the figure, V gene is firstly recruited for a site. J gene combines to the RAG complex after V gene.

It would be helpful if you could provide an actual excerpt from the text instead of a garbled summation. It's honestly hard to tell what your interpretation even is with some of the grammatical errors and use of incorrect terms to describe interactions.

The question is whether components of the RAG complex bind the RSS of V and J segments independently and then come together to form the complete complex or whether the RAG complex assembles completely on one one RSS and then binds the second.

Excerpt from Cellular and Molecular Immunology, 8th ED, p.181-182. Don't up-vote me, i just thought this text offers a good, up-to-date explanation.

The Mechanism of V(D)J Recombination
Rearrangement of Ig and TCR genes represents a special kind of non-homologous DNA recombination
  event, mediated by the coordinated activities of several
  enzymes, some of which are found only in developing
  lymphocytes, whereas others are ubiquitous DNA double-stranded break repair (DSBR) enzymes.Although
  the mechanism of V(D)J recombination is fairly well
  understood and will be described here, how exactly
  specific loci are made accessible to the machinery
  involved in recombination remains to be determined.
  It is likely that the accessibility of the Ig and TCR loci to
  the enzymes that mediate recombination is regulated
  in developing B and T cells by several mechanisms,
  including epigenetic alterations in chromatin structure
  and DNA as discussed earlier, and basal transcriptional
  activity in the gene loci.
  The process of V(D)J recombination can be divided
  into four distinct events that flow sequentially from one
  to the next (Fig. 8-10):
1. Synapsis: Portions of the chromosome on which the
  antigen receptor gene is located are made accessible
  to the recombination machinery. Two selected coding segments and their adjacent RSSs are brought
  together by a chromosomal looping event and held
  in position for subsequent cleavage, processing, and
  joining.
2. Cleavage: Double-stranded breaks are enzymatically generated at RSS-coding sequence junctions
  by machinery that is lymphoid specific. Two proteins encoded by lymphoid-specific genes, called
  recombination-activating gene 1and recombination-activating gene 2(RAG1and RAG2), form
  a  complex, containing two molecules of each protein,
  that plays an essential role in V(D)J recombination.
  The Rag-1/Rag-2complex is also known as the V(D)J
  recombinase.The Rag-1 protein, in a manner similar to a restriction endonuclease, recognizes the DNA
  sequence at the junction between a heptamer and a
  coding segment and cleaves it, but it is enzymatically
  active only when complexed with the Rag-2 protein.
  The Rag-2 protein may help link the Rag-1/Rag-2 tetramer to other proteins, including accessibility factors that bring these proteins to specific open receptor
  gene loci at specific times and at defined stages of lymphocyte development. Rag-1 and Rag-2 contribute to
  holding together gene segments during the process of
  chromosomal folding or synapsis. Rag-1 then makes
  a nick (on one DNA strand) between the coding end
  and the heptamer. The released 3′OH of the coding
  end then attacks a phosphodiester bond on the other
  DNA strand, forming a covalent hairpin. The signal
  end (including the heptamer and the rest of the RSS)
  does not form a hairpin and is generated as a blunt
  double-stranded DNA terminus that undergoes no
  further processing. This double-stranded break results
  in a closed hairpin of one coding segment being held
  in apposition to the closed hairpin of the other coding end and two blunt recombination signal ends being placed next to each other. Rag-1 and Rag-2, apart
  from generating the double-stranded breaks, also hold
  the hairpin ends and the blunt ends together before
  the modification of the coding ends and the process of
  ligation.
RAGgenes are lymphoid specific and are expressed
  only in developing B and T cells. Rag proteins are
  expressed mainly in the G0and G1
  stages of the cell
  cycle and are inactivated in proliferating cells. It is
  thought that limiting DNA cleavage and recombination
  to the G
  0 and G1
  stages minimizes the risk of generating inappropriate DNA breaks during DNA replication or during mitosis. Mice without functional Rag1
  or Rag2genes (Ragknockout mice) fail to develop B or
  T lymphocytes, and Rag-1 or Rag-2 deficiency is also
  a rare cause of SCID, in which patients also lack all
  lymphocytes.
3. Hairpin opening and end-processing: The broken
  coding ends are modified by the addition or removal
  of bases, and thus greater diversity is generated. After the formation of double-stranded breaks, hairpins must be resolved (opened up) at the coding
  junctions, and bases may be added to or removed
  from the coding ends to ensure even greater diversification. Artemisis an endonuclease that opens
  up the hairpins at the coding ends. In the absence
  of Artemis, hairpins cannot be opened, and mature
  T and B cells cannot be generated. Mutations in
  ARTEMIS are a rare cause of SCID, similar to patients with RAG1or RAG2mutations. (see Chapter
  21). A lymphoid-specific enzyme, called terminal
  deoxynucleotidyl transferase (TdT), adds bases to
  broken DNA ends and will be discussed later in the
  chapter in the context of junctional diversity.
4. Joining: The broken coding ends as well as the signal ends are brought together and ligated by a double-stranded break repair process found in all cells
  that is called nonhomologous end joining. A number
  of ubiquitous factors participate in nonhomologous
  end joining. Ku70 and Ku80 are DNA end-binding
  proteins that bind to the breaks and recruit the catalytic subunit of DNA-dependent protein kinase
  (DNA-PK), a double-stranded DNA repair enzyme.
  This enzyme is defective in mice carrying the severe
  combined immunodeficiency (scid)mutation, and mutations in the gene encoding this enzyme have also
  been discovered in human SCID patients (see Chapter
  21). Like Rag-deficient mice, scidmice fail to produce
  mature lymphocytes. DNA-PK also phosphorylates
  and activates Artemis, which, as mentioned before, is
  involved in end processing. Ligation of the processed
  broken ends is mediated by DNA ligase IV and XRCC4,
  the latter being a non-catalytic but essential subunit of
  the ligase.

Figure 8-10, Cellular and Molecular Immunology, 8e, p182.

If you downvote you should include an explanation.

Upvoted to bring balance to the force. Also all RSSes are not identical in the TCR/BCR genes. The RSS structure is a conserved heptamer followed by either a 12 or 23bp unconserved spacer, followed by a conserved nonamer. An RSS (12) and RSS (23) recombine much more efficiently than two (12) or two (23) sites. The direction and location of the (12) vs (23) sites facilitates the desired juxtaposition of a V site with a D/J site.


text:
Atrial contraction in complete SA block
In a complete SA block when there's block of impulse from SA node to Atrial syncitium, The ventricles start pumping at AV nodal rhythm but how do the atria then contract?

It depends.
It's likely that another point starts setting the pace instead of the SA node. More infos about cardiac pacing on Wikipedia
Or maybe different points try to set the pace contemporary, without generating a valid contraction but only electrical activity (such as in atrial fibrillation/AF, a very common disease mostly in elders).
An electrocardiogram could answer the question for the specific patient. If there is completely no atrial activity you'll find no P waves (no atrial activity) or baseline continuous little waves (in case of AF because of the irregular atrial activity) and probably bradycardia (because the pacer in the AV node is slower than the SA node).

Could you add some sources, please?

Done (as much as I could)

Looks much better! :)

What happens if the atria doesn't contract at all? like you said, no P wave. how does that effect ventricular activity?

If no contraction and no eletrical activity by the atria there is less efficiency in blood pumping (but you have to consider that normal atria do a little work compared with ventricular work).

Moreover if there is no atrial pacing, as I said in the answer, the rythm is slower than the normal one, reducing cardiac output ( https://en.wikipedia.org/wiki/Cardiac_output ) and with less response to exercise.


text:
Blood urea nitrogen and usage of proteins?
I have been reading some books and am getting slightly confused. Here is roughly what I have read.

The greater the blood urea nitrogen the greater the usage of proteins (since blood urea nitrogen is created via the metabolism of proteins).

and

A positive nitrogen balance (where nitrogen balance $=$ N intake $-$ N loss) indicates a greater usage of proteins.

To me these two seem to be contradictory, if you have greater blood urea nitrogen then surly you will have more nitrogen lost meaning the nitrogen balance would be more negative. So do these two statements contradict and either way please can you explain.

Well, nobody said N intake is a constant. Allow that to vary and you'll see that the balance can remain positive even with increasing loss

The quotes in the question provide incomplete information at best.
Let's focus on the nitrogen (N) that comes from protein, ignoring for now how metabolism differs among amino acids. We'll assume for simplicity that liver function is OK so that the urea N production rate is a reasonable measure of protein N degradation rate (say in units like moles of N per hour).
First, consider simple conservation of mass:

Intake = Loss + Net Storage

If you think about this in terms of protein N from the perspective of the whole body, you start to see the limitations in those quotes.
First, loss from the whole body of metabolized protein N in the form of urea N mostly occurs via the urine. Impaired kidney function may lead to less urea being excreted than is being formed. You will then have "Net Storage" of urea N in the blood and body fluids, so BUN can rise even if metabolism of protein is unchanged. In fact, BUN tests can be used with other tests to provide information about kidney function. Thus BUN levels don't necessarily tell you much about the urea N production rate or protein degradation rate.
Second, you have to consider that one "use" of proteins can be "Net Storage" to build muscle mass. That type of "use" won't show up in increased urea N production. Alternatively, body protein in muscle can be broken down to be "used" for metabolism/catabolism during an overnight fast, possibly leading to increased urea N production rate depending on how the mix of protein, fat, and carbohydrate catabolism has changed. Furthermore, the effects on BUN levels will depend on kidney function.
Both storage and degradation/catabolism are important "uses" of protein N, but they have different implications for production of urea N, and BUN levels don't necessarily represent the urea production rate.

Urea is the major nitrogenous end product of protein metabolism, and its production reflects both the dietary intake of protein as well as the protein catabolic rate. The magnitude of these processes have a similar influence on urea concentration in the blood stream. Please note, that BUN, aka blood urea nitrogen is a misnomer, here plasma or serum urea nitrogen is meant and not the urea concentration in the red blood cells.
Urea biosynthesis from ammonia is carried out exclusively by liver via urea cycle. As explained above, dietary protein intake as well as the protein catabolism end up with a certain amount of ammonia which converted to urea in the liver. This is why, the higher the protein intake, the higher the urea concentration; the more protein disintegrated via catabolism, the higher the urea concentration. The excretion of urea is carried out mostly by kidneys in a certain (almost constant) rate.
Now, the positive nitrogen balance means that in the system there is an increase of “net storage” of nitrogen (and we deal with azotemia). The important point is - the urea metabolism is a continuous event where two processes are going in almost (but not absolute) parallel: the urea production (liver) and urea excretion (kidneys). There is a constant “delay” between the urea production and urea excretion and if the organism is in high protein intake and/or high protein catabolism rate this delay will bigger. On the other hand, the bigger the excessive amount of urea, the more urea is excreted until its concentration is normalized. If the urea production will decrease (normal protein intake, normal metabolism), the system will eventually excrete the excessive amount of urea and nitrogen balance will be around zero value (never will be absolute zero though).  So,  if the blood sample from an otherwise healthy individual is taken in the middle of the explained cycle (higher protein intake/catabolism), there will be a positive nitrogen balance.
As can be seen from the explanation (I hope that it can), there is no contradictions between the clauses in the question.

The thing to remember is that no living system is 100% efficient. Firstly lets deal with your statement here:

A positive nitrogen balance (where nitrogen balance = N intake − N loss) indicates a greater usage of proteins.

Basically means what it says on the tin. If your body is utilising more nitrogen then it is giving out:

Positive nitrogen balance is associated with periods of growth, hypothyroidism, tissue repair, and pregnancy. This means that the intake of nitrogen into the body is greater than the loss of nitrogen from the body, so there is an increase in the total body pool of protein.

Now we really cant measure notrogen on a weighing scale. So the blood urea level is used as an estimator for nitrogen metabolism.
Now, as mentioned below, no system is 100% efficient, and the purpose of urea is infact to be as a vehicle to excrete toxic ammonia. Sure the body looses a few nitrogens in the form of urea, but as a whole, it gains a lot more from the metabolism.
An analogy:
In other words, think of it like this: When you make something out of wood (proteins), you get wood shavings (ammonia). Now you cant reconstitute the wood shavings back to a full wood (proteins), nor can you use wood shavings (ammonia) as they are toxic for you. So you group up the wood shavings (urea) and get rid of it.
The formula is essentially:
The number of furniture made = Function of (Weight of wood delivered - weight of saw dust taken out)
If you use a lot of wood (proteins), and are a good craftsman (healthy human)  you'll ultimately have a bit more shavings (blood urea nitrogen), but a lot more furniture to move around. Now since you cant see the furniture (proteins in tissues), but you can see the shavings coming out (blood urea nitrogen) there will be a rise in the BUN.
Now if you are a poor carpenter (disease or something), you mess up and you end up wasting a lot more wood as shavings than getting the furniture right. So for say 10 kilos of wood, you can only make one couch and 9 kilos of saw dust..  you are really not doing it right, and this is where the BUN gets in the negative territory (I know 10-9 is not negative, but remember the body has a baseline need of say 6 couches and you are only giving it 1, the body will get that from somewhere to the detriment if your health)
Apologies for the long winded analogy. I hope you understood what I was trying to imply. I am pretty sure someone out there will give a more scientifically accurate answer, so you might want to wait on that also.
Further reading from the wiki:

Amino acids from ingested food that are not used for the synthesis of proteins and other biological substances — or produced from catabolism of muscle protein — are oxidized by the body, yielding urea and carbon dioxide, as an alternative source of energy.
The oxidation pathway starts with the removal of the amino group by a transaminase; the amino group is then fed into the urea cycle. The first step in the conversion of amino acids from protein into metabolic waste in the liver is removal of the alpha-amino nitrogen, which results in ammonia. Because ammonia is toxic, it is excreted immediately by fish, converted into uric acid by birds, and converted into urea by mammals.
Ammonia (NH3) is a common byproduct of the metabolism of nitrogenous compounds. Ammonia is smaller, more volatile and more mobile than urea. If allowed to accumulate, ammonia would raise the pH in cells to toxic levels. Therefore many organisms convert ammonia to urea, even though this synthesis has a net energy cost. Being practically neutral and highly soluble in water, urea is a safe vehicle for the body to transport and excrete excess nitrogen.


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How does protein enter bloodstream?
If a hemophiliac patient injects his factor 8 through the veins directly into the bloodstream to provide the body with clotting factor... Why don't they just make the drug as a pill and have the liver do its job with extracting protein and dumping it into the bloodstream?

Likely a question for Health SE. But 'proteins do not survive the digest tract all that well' is the likely answer.

Why is that so?

Proteins will be digested through a number of proteases in the stomach and intestines (pepsin, trypsin, etc) into their constituent amino acids. The amino acids are then absorbed in the small intestine. So any specific proteins you try to put into a pill will be digested into amino acids before being absorbed. If you somehow manage to defeat the digestive enzymes, the protein will simply pass through the digestive tract without being absorbed--the intestines don't have the capability to allow larger polypeptides through.
If you think about it, this is probably a good thing. We don't want random proteins from our food running around in our bodies. It would likely kill us in short order.

Welcome to Bio. Nice answer,  but some references to allow for background reading are recommended


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Why does influenza sometimes cause GI symptoms?
I'm speaking strictly of influenza, not gastroenteritis which is sometimes mistakenly called "stomach flu." I just read this article on the mechanism through which rotavirus causes diarrhea and vomiting. Since the flu is a respiratory disease, through what mechanism does it sometimes cause diarrhea and vomiting? Does it also release proteins that activate the enteric nervous system in the gut? Is it caused by inflammation from cytokines being washed down the throat in mucus? Or is it the result of a secondary infection resulting from the decreased immune system?

Article: How influenza virus infection might lead to gastrointestinal symptoms Source study: Respiratory influenza virus infection induces intestinal immune injury via microbiota-mediated Th17 cell-dependent inflammation.
The idea is that Influenza virus infection originates in the respiratory tract. In response, the body produces these CCR9+CD4+ Th cells denoted Th17 in the lungs. Gut epithelial cells produce CCL25, a chemokine made to attract cells expressing CCR9 chemokine receptor. Th17 cells are a subset of T-helper cells that produce interleukin-17, more about that here. So what they found, is that the Th17 cells produced by influenza infection in the lungs migrate to the gut through this CCR9/CCL25 interaction, and they secrete cytokines that are meant to defend against infection. Of course, mucosal immunity at the gut epithelium is always active, because there are commensal bacteria there that out-compete pathogens among other roles.
Down in a section titled "Lung-derived CD4+ T cells destroy microbiota homeostasis and promote resident Th17 cell polarization" their conclusion is that IFN-gamma secreted by the lung-derived Th17 cells destroys the homeostasis of the gut microbiota, and cause other Th17 cells to become polarized in a way that they end up producing the specific set of cytokines causing the trouble in the first place. You also have to understand that the other cytokines the Th17 cells are secreting are causing tissue damage, leading to symptoms of intestinal disease concomitantly with what we've been discussing above.
I think that the process is just recently being illuminated so it may not be completely understood, either.

How are the lung-derived Th17 cells getting to the gut?

Generally, leukocytes in the lymphatics enter the blood through the left subclavian vein. Once there, they traffic to vascular endothelium expressing chemokine attractant molecules and utilize a number of adhesion molecules in concert to extravasate into the tissue expressing the attractant. This could mean multiple tissues given the right circumstances. The important thing to remember when i mentioned mucosal immunity is lots of effector cells are already there due to the presence of microbiota at all times, unlike the systemic response where effectors must be generated.
Here's a figure about extravasation, and another about mucosal immunity, and if you look here you can see that the Th17 lineage is under investigation due to it's inflammatory characteristics in autoimmune disease.

That's a complex process! How are the lung-derived Th17 cells getting to the gut? Is it migrating though the bloodstream, being swallowed? I guess I'm confused about how the common mucosal immune system mentioned in the article works.

@Tom I edited the answer to respond to your comment!


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What is the name for the opening in the mouth for the nasal passages?
Is there a proper anatomical name for the opening in the soft palette where the nasal passages enter the mouth?

Something other than oropharynx?

@skymningen From looking at drawings it looks like I'm talking about where the nasopharynx meets the oropharynx. There may not be a specific name for it. Sometimes openings have their own separate name (like the foramen magnum, or the anus, etc) but not always.

From what I understand from your comment is that you are asking for opening which connects the nasopharynx to oropharynx.
This opening is is connecting two parts of pharynx , acting like a bridge therefore it was named as Pharyngeal/Nasopharyngeal isthmus.
According to this site:

isthmus of pharynx
Type:Term
Definitions
  1. passage posterior to the soft palate by which the nasopharynx and oropharynx communicate (i.e., the junction of nasopharynx and oropharynx), closed during swallowing by elevation of the soft palate and contraction of the posterior fascicle of palatopharyngeus (muscle), forming a Passavant cushion.
Synonyms
  isthmus pharyngis , pharyngeal isthmus

Source of image: Textbook of Anatomy: Head, Neck, and Brain : Vishram Singh


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What is the difference between fixation and loss of alleles in a population?
When running a simulation in PopG, with parameters:

Population size: 100
AA fitness: 1.0
Aa fitness: 1.0
aa fitness: 1.0
Mutation A to a: 1.0E-6
Mutation a to A: 1.0E-6
Migration rate between populations: 0.001
Initial frequency of A: 0.5
Generations to run: 1000
Populations evolving simultaneously: 100
Random number seed: autogenerate

I get a result of 20 populations being fixed and 10 populations being lost. Obviously, as this is a simulation, these results will vary each run; but what I am having trouble understanding is are lost populations just fixation of the recessive a allele?

I'm voting to close this question as off-topic because the question was specific to the OP and the OP abandoned the question, has provided no feedback to the answerers as to why their answers were not sufficient, and has had no subsequent activity on the site.

I don't think this is a valid closure reason. As irritating as it is for the work to go seemingly unappreciated by the OP, they have no obligation to feedback, and Fileunderwater appears to have grasped the question and given an answer that suits, which is therefore still useful to the site.

Yes, 'lost' seems to be referring to fixation of the a allele in this program, where the statements 'fixed' and 'lost' are specifically referring to the A allele. Conceptually, 'fixed' and 'lost' are describing the same thing in this particular case ( since you only have two alleles in the population) - the loss of one allele in a population.

Note that once the plot of the gene frequency curves reaches the right-hand side of the graph, the program prints there the number of populations that fixed for the A allele (ended up with a frequency of 1.0) and the number that lost this allele.

(my emphasis, from http://evolution.gs.washington.edu/popgen/popg.html)

Lost vs fixed population
I am not sure I understand your question. It seems to be a matter of definition. The term lost and fixed populations sounds quite wrong. I have never used PopG. Is the PopG manual using these terms without defining them?
Probability of loss and probability of fixation
Given your parameters, you will clearly expect that, if fixation occurs, then it is as likely that the allele a fixes than the allele A fixes. In other words, the probability of loss and the probability of fixation for a neutral locus are equal if you start at frequency 0.5.
Did you say recessive allele
Note that there is no recessive allele at least in terms of fitness (but you probably don't have an explicit phenotype that is afterward link to these fitness values anyway) in your simulation as all genotypes have the same fitness.
Extra info: $F_{ST}$
If I understand your parameters correctly, you are simulation an island model with constant migration between any two populations with D=100 populations. In such circumstances, the $F_{ST}$ should be $$F_{ST}=\frac{1}{1+4N(m+\mu)\left(\frac{D}{D-1}\right)^2}$$ which is approximatively equal to $\frac{1}{1+4Nm}$, where $m$ and $\mu$ are the migration and mutation rate respectively.
Because of migration, you wouldn't expect that all population would be fixed for one or another allele at any time point.


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Examples of physiological differences between isolated & non-isolated individuals
I'm looking for examples of organisms (or biological units at some other scale, like cells) whose physical and/or behavioral properties develop differently depending on whether the individual is in close contact with others. In particular, I'm interested in cases where individuals are specialized for fairly narrow functions as part of their usual collective existence (e.g. as animals in a society or cells in a tissue) but develop facilities for more autonomous/self-sufficient operation (possibly including significant anatomical changes) when isolated.
The example that originally came to mind (which isn't really even what I'm looking for) is heart cells that beat together when touching. A slightly better one might be colonial organisms like pyrosomes. I hope there are even better examples in which the "solitary" form exhibits distinct differences from the "grouped" one. Are there animals or plants that do this? Microscopic organisms (maybe other zooids)? Thanks in advance.
(Sorry if this question is too vague/abstract. For more context: I'm helping a friend with some nonfiction writing, and we're looking for a metaphor from nature to introduce a passage about how pandemic-related isolation has spurred some people to "blossom" artistically/intellectually/etc.; it'd be really cool if there were an organism that similarly "grows into a new version of itself" when separated from its neighbors.)

I think it would be helpful to explain your goal; otherwise it's a pretty broad question that could possibly be answered any number of ways, which isn't a good format for a SE question.

Thanks for the feedback! Edited to explain my goal.

Just for info, we have a [worldbuilding.se] site as well as a [writing.se] site -  this question might have easily fit on the former, more-or-less as is.

Thanks! A fictional example of what I'm describing wouldn't be as compelling as a real one from biology, so I'll leave my question here unless it's deemed not appropriate.

You can ask for a "finite list" of real-life examples, but you'd need to specify environment and such. Worldbuilding uses real science to create fictional worlds (and, to be fair, there's quite a few magic related ones too). Not an answer to this, as it's late for me to start writing answers, but what leapt to mind immediately on reading it was slime molds, worth a read.

Welcome to Biology.SE. Please take the [tour] and then go through the [help] pages starting with [Ask] questions effectively on this site and [edit] or delete your question accordingly. I have voted to close this as needing focus — this is a question that would require a textbook to answer, which is both impractical and expressly off-topic for this site. In addition, as currently written the cells in any multicellular organism would seem to fit your criteria, as would any social organism. Plants also grow differently when crowded vs. isolated — e.g. compare tree farms to isolated trees ...


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Is there any methods to avoid the pcr control contamination?
Why do I use the primers in the D1-D2 region to amplify the fungus, and using water as a negative control has a weak band that is the same size as the target fragment? When using the ITS primer, using water as a negative control in the ITS region, there is no band. why does this happen?

Can you add some more information on the regions and also your protocol? What do you do for the PCR and how do you do your controls.

I use the NL-1F and NL-4R primers to amplify the D1-D2 region of fungi, using the Thermal cracking method to obtain the fungi DNA template. Control does't add DNA template. PCR program is 95℃ 5min, 95℃  30s, 51.5℃ 30s,72℃ 1min,72℃ 5min, 4℃.36 cycles. The electrophoresis result is that the control has a weak band. I use the ITS1-F and ITS4-R primers to amplify the ITS region. Only change the annealing temperature to 55℃。The control doesn't have band. why does this happen?

It would be great if you could use the edit function to add this information to the question. To understand this right, if you amplify the D1-D2 region and use water as a negative control you get a weak band, when you do the same blank control on the ITS region (with the ITS primers of course) you get a blank negative control?

yes, i use water as a negative control has a weak band that is the same size as the target fragment, when amplifying the D1-D2 region? When using the ITS primer, using water as a negative control in the ITS region, there is no band. why does this happen? thank you very much.

I think you have a contamination problem. Most likely the primer used to amplify the D1-D2 region are contaminated with your DNA. This can happen easily and underscores the importance of proper negative controls.
Since your negative control with another gene is clean, this points against a contamination of your other reagents (dNTPs, water) or even your pipette (yes, this can happen and I have seen this in the lab). Otherwise the negative control of this reaction would show a band as well. I suppose that all reagents except the primers are the same for both reactions, so this clearly points to a contamination of the primers.
This is easy to solve: Make a fresh dilution of your primer working stock - preferrably at another working space where you do not work with your fungal DNA. If possible use filter tips when doing PCR work to avoid cross contamination of samples.

I don't think you can say where the contamination is and would treat all reagents and pipettors as potentially contaminated. The contamination could be  D1-D2 PCR product which would explain the other control being OK.

@Michael_A I would agree, if the negative control of the other gene would also show a band. Since it doesn't (and I suppose that all reagents except the primers are the same between these two reactions) this is highly unlikely.

I agree with Chris. You don't want to have handled amplified PCR product at the same workstation (or with the same pipettes) used for setting up reactions or diluting primer stocks. Filter tips are strongly recommended. And I'd also consider decontaminating all of your work stations and pipettes with a diluted bleach solution or something like DNAzap (check pipette user manual for cleaning instruction first to make sure it won't cause damage, but shouldn't).


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Are color-blind carriers partially colorblind?
Since color-blindness passes along an recessive gene in the X-chromosome, women are rarely affected, while men are affected more frequently. Women with one copy of the color-blindness gene are said to be "carriers". Women also have something called a "genetic mosaic", due to X-inactivation in the early stages of development. However, which X-chromosome is inactivated depends entirely on chance. My question is, what happens if some of the cone cells in the eye contain a copy of the X-chromosome with the color-blind gene? Will the woman be partially colorblind? I read somewhere that the woman's brain learns to ignore signals from the cone cells that are affected. Is that true?
Sources

X-inactivation and color-blindness
As mentioned in this article,

As we [women with the recessive allele] have several millions photoreceptors (cones) which are responsible for our color vision, the defective signals are in a way oversteered by the correctly working ones.

Edit: In the original post, I also included a follow up question about why color-blindness is still present in the gene pool, but that is answered in this question, so I removed it.

Best practice is to ask one question per post. In addition, I think your second question will find an answer here. If yes, (it does address evolution, camouflage etc.), you might be able to focus your post better by eliminating part II. Adding your sources to part I is important; a Q close vote has been posted, because it seems like you haven't added background research, which we ask every person to do on this site (note that I am quite convinced you did prior research, but please add the relevant links to better frame your question).

Thanks a lot! Like I mentioned in my post, I remember reading about this elsewhere, but I can't seem to find the link now. A mistake on my part. I will try my best to provide relevant links in the future.

Looking at the literature, I find the following passage in a review of the genetics of colorblindness:

Females have two X-chromosomes, and can either be homozygous or heterozygous for the X-chromosome opsin allele. If homozygous, they are dichromatic; however, females who carry both an allele for an L opsin and one for an M opsin have the equivalent of normal human color vision, having both L and M cones because the process of X-inactivation segregates the expression of the L and M opsin genes to separate populations of cones. The significance of this is that in trichromatic female squirrel monkeys, the difference between L and M cones is solely determined by the stochastic choice of which X-chromosome is retained as the active one. Variation in L:M cone ratio in female squirrel monkeys is similar to what is seen in human males with normal color vision. In squirrel monkeys the variation has been attributed to the stochastic process of X-inactivation, influenced by the number of cells present at the time of activation and other random factors in the inactivation process (Jacobs & Williams, 2006).

Boiling this down: X-inactivation happens at a local enough scale that eyes of heterozygous females have active versions of both normal and mutant opsin genes. So they will still see color "similar to what is seen in human males with normal color vision".
Note of course that people with an XX complement can have better possible color perception than XYs, as they have the potential for tetrachromacy:

females who are heterozygous, for example, having OPN1LW genes that encode two spectrally distinct L pigments, would have four different cone types -- two different L, plus M and S -- and thus the potential for having tetrachromatic color vision (Bosten, Robinson, Jordan & Mollon, 2005, Jordan & Mollon, 1993, Jordan & Mollon, 1997). Prior to the discovery of variation in peak sensitivity of pigments underlying normal color vision, it had been appreciated that female carriers of a red-green color vision deficiency have the potential for tetrachromatic color vision (Nagy, MacLeod, Heeyndermann & Eisner, 1981).

Here is a study specifically on color perception in heterozygous women that may answer further questions.
So there are some differences between color perception of heterozygous XX vs XY, they're just not colorblind per se.

ZO-Bro, your second paragraph considers why colorblindness stays constant in the gene pool.  Whether it is an advantage or not in some situations, if it is not really being selected for or against, it will probably hang around indefinitely in roughly the same frequency. Nearsightedness would probably disappear FROM THE POPULATION if we lived on the savanna with only spears and stones.

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text:
What does cell-to-cell variability means?
I'm reading an article where they claim that transcriptional bursting could play a role in cell-to-cell variability.

Cell-to-cell variability plays a critical role in cellular responses and decision-making in a population, and transcriptional bursting has been broadly studied by experimental and theoretical approaches as the potential source of cell-to-cell variability.

I was looking for a definition of Cell-to-cell variability and I found only the one of Single-cell variability

In cell biology, single-cell variability occurs when individual cells in an otherwise similar population differ in shape, size, position in the cell cycle, or molecular-level characteristics. Such differences can be detected using modern single-cell analysis techniques. Investigation of variability within a population of cells contributes to the understanding of developmental and pathological processes.

I won't ask a question that's related to an article before reading it completely! The answer was in the first paragraph.

Cell-to-cell variability defined as when genetically identical cells in an identical environment behave differently, leading to significant consequences in many biological processes from bacterial decision-making to mammalian development.