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How does Natural Selection shape Genetic Variation?
Background
Importance of the additive genetic variance
As stated here, the fundamental theorem of Natural Selection (NS) by Fisher says:

The rate of increase in the mean fitness of any organism at any time ascribable to NS acting through changes in gene frequencies is exactly equal to its genetic variance in fitness at that time.

NS reduces the additive genetic variance
On the other hand, NS reduces additive genetic variance (discussion about the origin of this knowledge can be found here). The genetic variance of a population for multiple traits is best described by the G-matrix (here is a post on the subject).
What is a G-matrix
A G-matrix is a matrix where additive genetic variance of trait $i$ can be found at position $m_{ii}$. In other words, the diagonal contains the additive genetic variance for all traits. The other positions $m_{ij}$, where $i≠j$ contains the additive genetic covariance between the traits $i$ and $j$.
Question
How can one model how the G-matrix changes over time because of selection (assuming no mutation)?

Great question - I know there is some theory on it, I will do some reading on it but I'm off to a quantitative genetics course tomorrow so maybe I'll have a good answer after that!

You can perhaps ask how can it be modeled instead of "is there a model". In any case the question boils down to - how does a selection operation (random sampling) affect covariance matrix. This is more of a statistical question.

Post edited! Yes, indeed the one who wish to answer this question will probably need some knowledge in statistics.

First of all, here is a program which simulates the evolution of the G-matrix over multiple generations, it's a few years old (they seem to have stopped developing it) and I've only played with it briefly. This could solve how to model the evolution of the G-matrix.
Fisher's fundamental theorem is a great place to start off with the theory of this:

The rate of increase in fitness of any organism at any time is equal to its genetic variance in fitness at that time.

What this means (as I am sure you realise but I will put in so the answer can help others too) is that evolution by selection depends not only on the strength and form of selection, but the genetic variation underlying the selected trait. This is captured in the breeders equation $\Delta \bar z = G \beta$  where $\Delta \bar z$ is the response (in a multivariate space), $G$ is a matrix of the genetic variance within traits covariance between traits (different traits, the same traits in either sex, or the same traits in multiple environments) and $\beta$ is the vector of selection gradients on all of those contexts. It seems reasonable to expect that given enough time selection will erode variation because standing genetic variance is a finite resource and selection removes polymorphism while not adding any new variants (that's for mutation & migration).
This paper discusses the effects of both selection and drift on the G-matrix, they also deal with some modelling to support their results. More specific to simulation, this article by Arnold et al (a number of the big players in the G-matrix circle). It reviews "empirical, analytical, and simulation studies of the G-matrix with a focus on its stability and evolution." It would be a really good read for you on this subject.
This paragraph captures the essence of your question:

Focusing on a longer time scale, we find that the G-matrix evolves in expected ways to the AL [adaptive landscape] and the pattern of mutation. In the absence of correlational selection (rω = 0) and mutational correlation (rμ = 0), the average G-ellipse is nearly circular, although the ellipse fluctuates wildly about this average (first row in Fig. 6). At the opposite extreme, when the leading eigenvectors of the AL and the M-matrix [mutation matrix] are both inclined at an angel of 45°, the leading eigenvector of G is pitched at the same angle (last row in Fig. 6). Between these two extremes, G tends to evolve to a shape and orientation that represents an intermediate compromise between the AL and M. In other words, the simulation results confirm our intuition and theoretical expectations (Lande 1980b) that G should evolve toward alignment with the AL and M.

Simulation studies of the G-matrix:

Bürger R, Wagner GP, Stettinger J. How much heritable variation can be maintained in finite populations by mutation-selection balance. Evolution. 1989;43:1748–1766.
Multivariate mutation-selection balance with constrained pleiotropic effects.
Wagner GP
Genetics. 1989 May; 122(1):223-34.
On the distribution of the mean and variance of a quantitative trait under mutation-selection-drift balance.
Bürger R, Lande R
Genetics. 1994 Nov; 138(3):901-12.
Predicting long-term response to selection.
Reeve JP
Genet Res. 2000 Feb; 75(1):83-94.

The last article there by Reeve is probably the best paper for your question because it describes in some detail the simulation model they use and how it is all set up. Briefly they simulate a population of 4000 diploid individuals with three genetically correlated traits with separate but identical sexes, random mating, and discrete generations. 20000 generations are simulated to allow mutation-selection-drift equilibrium (almost like a burn-in time on an MCMC chain). They then shift the optimum for one trait by 10 standard deviations and simulate 1500 generations in five replicates. There are 100 unlinked loci underlying the traits, with 50 loci affecting each trait (randomly assigned) meaning there is likely some degree of genetic correlation though it is not perfectly correlated (for some reading on genetic correlations and the evolution of differences you can read Bonduriansky & Rowe 2005, Poissant et al 2010, and Griffin et al 2013). The model then assigns phenotypic values to individuals, and fitness is derived. Figure two shows how the mean, skew, and kurtosis of the variance distributions changed for those 1500 generations.

Addition
Roff 2012:

"While the mean trait values change under selection, so also will the
  G matrix, its orientation tending to shift in the direction of
  selection. ... Genetic drift may also play a role in changing the G
  matrix, but in this case the change will be random though on average
  producing a proportional change in the constituent variances and
  covariances."

nice reference.. I got some insight

Yeah I quite like that Reeve paper and the Arnold paper @wysiwyg - quite good papers on the fundamentals of the g matrix

Very sweet @GriffinEvo +1. I will definitely read the articles you cite. I am glad we can ask such a bit advanced questions and get answers that will largely ease my entry into this topic.

I am currently entering the topic too - working on G-matrix and multivariate breeders equations for a research visit! @remi.b

I am presenting a speculative approach since nobody has mentioned about any existent models yet.
Assuming that selection is based on performance in certain tasks; performance is a function of traits which in-turn is a function of genotype. Performance is a non-linear function of genotype and selection imposes a cutoff/bandpass filter on the performance vector. So selection causes some individuals to perish — which genotypes are selected out depends on their relative contribution to the performance function. As you already mentioned in the question, selection would lead to reduction in variance; some of the diagonal terms would reduce. Now if your traits are truly independent (as in case of additive variances) and also uncorrelated then then extradiagonal terms would be very small and their contribution to the eigenvalues would be minimal.
Overall the eigenvalues and hence the determinant of the G-matrix would decrease upon selection.
Addition based on the points mentioned in rg255's answer
The paper mentioned by rg255 talks about the shape of the distribution corresponding to G-matrix.

The eigenvalues correspond to the axes of the ellipse. In the first case eigenvalues are 0.5 and 0.5; in the second case they are 0.05 and 0.95.

Alternatively, assuming a normal (Gaussian) bivariate distribution of
  values, we can represent the cloud with a 95% confidence ellipse whose
  axes represent the principal components or eigenvectors of the
  G-matrix (Fig. 2). The length of each axis is determined by the
  corresponding eigenvalues of the G-matrix.

Selection may reduce the area of the ellipse if the boundary points get selected out, hence causing eigenvalues and determinant to reduce. However, if the central points are removed (some kind of inverse-bandpass filter), then the limits of variation would not change. In other words the shape or size of the ellipse would not change — it would just become sparse.


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Coefficient of relationship and path of coefficient
A path of coefficient of relationship is defined as
$$\rho_{AO} = \left( \frac{1}{2}\right)^n \sqrt { \frac{1+f_A}{1+f_O}}$$
This SE post discusses this definition
From this, the coefficient of relatedness between two individuals $B$ and $C$ is defined as
$$R_{BC} = \sum \rho_{AB} \rho_{AC}$$
, where $A$ is (I think) the last common ancestor of $B$ and $C$. The sum is over all possible path coefficients.
Source: Wikipedia

I am a little bit confused, I don't really understand this formula. One reason is the following. Let's assume that  $B$ has 2 paths and $C$ has 3 paths to go to $A$. If we denote $\rho_{AB,i}$, the path $i$ (or the $i^{th}$ if you prefer) between $A$ and $B$,
$$R_{BC} = \rho_{AB,i} \rho_{AC,i} + \rho_{AB,j} \rho_{AC,j} + \rho_{AB,k} \rho_{AC,k}$$
But the path $\rho_{AB,k}$ does not exist because there are only 2 paths between $A$ and $B$ (which are denoted $i$ and $j$). Also, there is no reason to count the path in a specific order and not another one. If we change the order we count the paths between $C$ and $A$, we can get:
$$R_{BC} = \rho_{AB,i} \rho_{AC,j} + \rho_{AB,j} \rho_{AC,i} + \rho_{AB,k} \rho_{AC,k}$$
, which is obviously different from the previous calculation of $R_{BC}$
Can you help me making sense of these formulas?

http://www.genetic-genealogy.co.uk/Toc115570135.html. The notation is confusing and the Wiki site is not helpful (imo). This site is better (many examples) and mentions Wright's original paper.

It would be more like: $\sum_i (\rho_{AB}\rho_{AC})_i.$

Wright's 1922 paper. http://aipl.arsusda.gov/publish/other/wright1922.pdf

Your comments and links helped a lot! Thanks. genetic-genealogy offers a perfect "for dummies introduction" I don't quite know how to answer my messy question though. You can give a try if you want and I'll check it. Otherwise I might just delete it. I still don't understand this and that though.

The expression $f = 2h-1,$ coefficient of inbreeding (COI) is a measure of homozygosity. Since in a randomly breeding herd (of cattle) we expect 50 per cent heterozygous and 50 per cent homozygous, the minimum for $2h-1 $ is 0. If the cattle's genome is purely homozygous (aa, AA) we have $2h-1 = 1.$ (h is total homozygosity--see Wright's paper, linked below.)
As we can see from this site, a basic calculation of relationship coefficient may not deal with f at all. For two descendants B, C, the quantities $f_B,f_C$ are an attempt to factor in existing relative homozygosity that the coefficient of relation (COR) would otherwise not capture. Likewise $f_A$ measures preexisting homozygosity in the common ancestor of B and C. If animal A is the product of siblings then the homozygosity could already be quite high and this would maybe have measurable effects on the vitality of a cross between B and C.
Now $f_A$ and $f_B$ vary between 0 and 1 so $s = (\frac{1+f_A}{1+f_B})^{1/2}$ varies between $(1/2)^{1/2}$ and $(2)^{1/2}.$ Note that the important thing here is relative homozygosity of an animal and its ancestor:
a. If the ancestor A and descendent B have the same known preexisting burden of heterozygosity we can disregard s (and f) entirely. Their COR will depend only on path distance.
b. The homozygosity of the ancestor A  tends to increase COR while that of B tends to decrease COR.
The expression $r_{BC }= \sum p_{AB }\cdot p_{AC}$ is somewhat confusing. On page 334 of one of Wright's earlier papers we can get a clear idea of the use of the coefficient.
He defines $p_{BA} = (1/2)^n (\frac{1+f_A}{1+f_B})^{1/2}.$ If the path from C to A is $p_{CA} = (1/2)^m (\frac{1+f_A}{1+f_C})^{1/2}$ then the total path BAC would be
$$ p_{AB,AC} = (1/2)^{n+m}(\frac{1+f_A}{1+f_B})^{1/2}(\frac{1+f_A}{1+f_C})^{1/2} $$
$$= (1/2)^{n+m}\frac{1+f_A}{[(1+f_B)(1+f_C)]^{1/2}}  $$
So the expression for the sum of such paths would be
$$r_{BC} = \sum_i p_{AB,AC} = \sum_i (1/2)^{k_i}\frac{1+f_{A_i}}{[(1+f_B)(1+f_C)]^{1/2}}   $$
in which $A_i$ is the ith ancestor through whom B and C are related. The total path length for a given term is $(n_i+m_i)$ which I abbreviated $k_i.$
So a less confusing expression for $r_{BC}$ might be:
$$r_{BC }= \sum_i p_{A_iB}p_{A_iC}. $$
Note that the sum is over all common ancestors back to some arbitrary generation.
A good example of this is Figure 11 at link 1 above.
It's really not ``dumbed down'' at all, it just leaves out the factor s, which for a carefully maintained herd may be close to 1 anyway.

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Is the male bee's penis homologous to the female bee's stinger?
Considering that when a bee stings it loses its stinger and dies, this is similar to the male drone losing its penis and dying after copulation. It also seems similar that each event basically rips the abdomen open. Are the two structures a homologous pair?

Not sure why the downvotes. Is this question off topic here?

Shouldn't be off topic. It actually is a very interesting question. +1 @AlwaysConfused: Of course it's a penis ... what else should it be?

@AlwaysConfused http://biology.stackexchange.com/q/45465/16433

After a little bit of digging I was able to find a couple of facts that seem to verify that the drone bee's penis is in fact homologous to the worker bee's stinger:
This Wikipedia article about the stinger that says a honey bee's stinger is "a modified ovipositor as in other stinging Hymenoptera".
This book (actually about soil arthropods) states very specifically that, "The ovipositor, with which the female lays her eggs, is homologous to the male's penis.".

That is the very best explanation for why male bees do not have stingers (which I have been asking myself on several occasions). Thanks!

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Cell evolution: immortality vs reproduction
Many sci fi movies produce interesting ideas and technologies that we seem to be able to realize in real life at some point. "Lucy" was not one of those movies.
But Morgan Freeman's speech in the movie on cell evolution did interest me.
The speech claimed that cells in harsher environments evolve towards immortality, while cells in favorable environments evolve toward reproduction.
Is this idea accurate?

Just for the pleasure to hear Morgan Freeman's arguments, can you please link the video of his speech?

How would you compare survival to immortality? There are many examples of adaptation for survival, but immortality is a stretch.

@Remi.b I would like to; I welcome someone to find this clip - It doesn't seem to live on Youtube yet.

@anongoodnurse I think "immortality" isn't meant literally. It's a dramatization for increasing lifespan.

You may want to read a bit about the evolution of ageing. This post for example is very interesting (it won't necessarily answer your question though).

In Nick Lane's book Life Ascending he talks about caloric restriction resulting in more mitochondria in cells and less mitochondria leak. This is a stress response that may inhibit cell degradation (death). I'm sorry I don't remember who the researchers were who discovered this or theorized on it, but I thought it might be germane to this question.

It wouldn't be good to replace reproduction with immortality even if it were possible. Let's assume some animal was immortal, could not die of old age or disease. There would still be accidents, injuries, starvation, or predators to worry about, so they would still have to reproduce to keep the species going.

"All the cells that make up the worm or human has only two options ...
Immortality ...
Or reproduction.
If its habitat is not quite favorable ...
The cell chooses immortality ...
That is to say, self-sufficiency, self ...
But if the habitat is favorable ...
This is the reproduction is selected.
And when they die the essential data is passed to the following cells ...
Who in turn pass on these cells ...
The knowledge, knowledge is devised through time."
http://www.springfieldspringfield.co.uk/movie_script.php?movie=lucy  I found the script, no video though.

You'll see that in many cases, when any sort of cell enters a zone of intolerance or zone of physical stress, the replication machinery gets put on the backburner (and thus replication). Expression of stress-response proteins like heat shock proteins is increased as a result (1). If a cell isn't within acceptable parameter to undergo division at G1 or G2 (anoxic environment, etc.), you'll find mechanisms like G0 phase or sporulation are preferred until the environment returns to something less stressful (2). I wouldn't say cells would rather be immortal, per se, but longevity or even apoptosis/entosis/etc. would be preferable to replication if nothing is going right (3, 4).
To be clear, when we're talking about evolution that's a tough one. Sure, some sort of stress-response transient signal could induce some lasting cell memory selecting toward a specific function. I simply don't have the data to quote you in that aspect, however.

Biology of the heat shock response and protein chaperones: budding yeast (Saccharomyces cerevisiae) as a model system.
Slonczewski, J., & Foster, J. (2011). Microbiology: An evolving science (2nd ed., p. 143). New York: W.W. Norton.
DNA damage-induced apoptosis
Cellular Stress Responses: Cell Survival and Cell Death

As a footnote, while replication does occur in sporulation, the replicated chromosome is destroyed in the process of forming the actual spore.


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How does vasoconstriction/vasodilation change blood pressure?
Background: I am coming at this question from an electrical engineering background, and I feel like I am missing certain assumptions that are going into the statement found in my physiology textbook, "vasoconstriction increases blood pressure"."
Consider a simple series circuit and a parallel circuit run by a battery/heart [you will find the parallel and series circuit in any physiology book description of the vasculature, yet I can't find any exploration of the assumptions made when applying these circuit models]:

In the series circuit, if I have an increase in resistance across
one of my resistors, this will basically redistribute the pressure
drops across the resistors, but it will not alter the total pressure
drop across all the resistors [fixed by the heart].
In the parallel circuit, if I have an increase in resistance across
    one of my resistors, this will redistribute the flow to different
    branches, but the pressure drop will not change as again this is
    fixed by the heart.

This analysis seems to suggest that if the resistance across an organ [branch of parallel circuit] changes, the flow changes, not the pressure. The heart, I would assume, then responds by increasing the pressure to increase flow ie actually injecting energy into the system.
Here is the problem with the circuit model though:

it assumes that the battery/heart is the only source of energy in
the system, and the resistors are passive re distributors of that
energy.
the controllers of vascular resistance are smooth muscle which must actively put energy into the system to vasoconstrict. This could be
a source of pressure increase as the smooth muscle would be actively
constricting against an incompressible fluid, but I am really not
sure.
it does not account for the compliance of the vasculature.

-the tubing the heart is hooked up to modifies the blood pressure the heart has to generate to inject fluid into that tube. If the tubing was stiff, the heart would have to generate very high systolic pressures that would then rapidly decrease during the diastolic phase. The more compliant the tubing, the less pressure the heart has to generate to inject fluid into the tube. Intuitively though, there would seem to some relationship between the ability of a fluid to flow and vessel compliance. A highly compliant vessel with a fluid injection will simply expand and hold the fluid while a less compliant vessel will maintain a pressure necessary to push the fluid along.
Sparknotes in the form of questions:

Is the only source of energy in the cardiac circuit the heart? Or
does artiole smooth muscle actually inject energy into the system,
        and result in systemic increases in the pressure available in the
        closed circuit.
I don't think vascular compliance ie expansion of the artery walls
due to volume filling results in any active injections of
        energy into the system..it should simply transfer the energy
        available to push fluid to elastic energy in the connective tissue
        of the artery walls. Is this correct?
Does vessel compliance partly determine the pressure the heart has to inject into the system?
What is the relationship between compliance and flow if there is one?

How do say pressure drop is fixed by heart?

Its  engineering lingo..I apologize. It essentially means that the only energy in the system is provided by the heart.

I mean, if you increase a single resistance in a series circuit, will there be no change in the potential drop across the entire circuit?

correct by conservation of energy

The circulatory system is a dynamic system which cannot be adequately explained by your example (at least not by me). You need to understand it, not seek to make it fit your (especially) electrical circuits with resistors. Blood isn't electricity. At least try a fluid dynamics model.
Let's take this very simple model: Blow up a balloon four-fifths of the way, and put a wide inflatable cuff around its middle. Inflate the cuff so that the balloon bulges just a tiny bit at the ends, then stuff it all into a plexiglass box so that the balloon has no room to expand. The plexiglass box represents our body. Lets call the pressure inside the balloon now normal blood pressure. The air in the balloon represents your total blood volume. It can't change from moment to moment; it's fixed. The box can't change it's volume moment to moment either. It's fixed.
The cuff represents arterial smooth muscle. Vasoconstriction can be represented by inflating the cuff further. Constriction (inflation of the cuff) will increase the pressure throughout inside the balloon, because the same amount of gas now has to exist in a smaller space. Vasodilation (deflating the cuff) decreases the pressure inside the balloon, because the gas can now inhabit a larger amount of space.
That's it, really. If the same volume must inhabit a smaller, constricted space, the pressure exerted by blood in that space will be higher. If the blood vessles dilate, the pressure in the blood vessels falls.
Now add about 20 layers of complexity to that simple model, and you have a working model of the circulatory system.
Sparknote answers:

Arterial and arteriolar smooth muscle "injects energy into the system", resulting in systemic increases in the pressure existing in the vascular "circuit" (meaning somewhat elastic tubing) if resistance requires energy. (So I have misunderstood: see @Raoul's answer.)
Sorry, I didn't read this properly the first time around. Yes, the heart supplies the energy. The contribution of the elastic walls of the arteries is not active, but passive.
Absolutely. The more elastic/compliant the arteries are, the less work the heart must exert to pump the blood through the circuits. The stiffer and narrower the arteries are, the harder the heart must work to pump blood through the circuits. The result of that increased work is a thickening of the muscular walls of the heart, called ventricular hypertrophy, which is a sign of elevated pressure in the system.
I'm not sure I want to commit here to your lingo, but the answer should be inferable from numbers 1-3. Elastic vessels help (by rebound compression) to propel the blood through the circuits. Stiff vessels hinder it, making the heart do more of the work.

I am not an engineer, so I may be misusing some of the terms.
Edited to add: Please see @Raoul's answer for a better explanation.

I'll try a brief answer myself.

No, the heart is not the only energy provider, as others have stated above. Does vasoconstriction inject energy into the system? Not really. Arteriolar constriction will increase the resistance of the system. Therefore, more energy will be required to keep flow at a constant level when vasocontriction occurs. Arteriolar vasoconstriction forces the system to function at a higher energy level, yet it does not inject energy targeted at facilitating flow.
Yes, your assumption is correct.
@anongoodnurse answered correctly.
There is no direct relationship between compliance and flow. They are independent factors. The important point is the following: during diastole, the heart is isolated from the vessels. The higher the vessel compliance is, the more potential elastic energy will be transferred from the heart to the vessels during systole, to then ensure good flow during diastole. In elderly persons for example, arteries are usually stiff, systolic pressure is high, and diastolic pressure is low (as is flow).

To conclude, I would say that the most important lesson that is to be learned here is that although a higher blood pressure means a higher energy state and more work for the heart, it is incorrect to assume that blood flow is physiologically adequate because pressure is high! This is a common mistake made in the emergency room.

+1 - glad to read your answer. You understand fluid dynamics better than I do. Because of your different answer, I had to rethink my own, and see my errors. I do find myself sometimes wishing you were around more. Care to weigh in on the cardiac output question? ')

@anongoodnurse Thanks! I'll have a look at that one. I spend a lot of time on stackoverflow, but I like it here as well. I'll definitely stick around. BTW, your answers are usually very good!

I just want to add a few points to the above answer:
Heart is not the only organ which helps blood flow. The following structures also help:

The action of muscles on deep veins acts as a pump - Soleus is called peripheral heart for that matter
The compliance itself adds to the flow - Infact the compliance of the blood vessels is what makes the blood flow continuous instead of pulsatile like a system with stiff tubes would be expected to act when the pump is pulsatile in nature

Some Critical Points to keep in mind:

The circulatory system is made in such a way that the total sum of cross sections of all the vessels at a particular level is as follows:

The sumtotal of cross-sections of all capillaries is the largest cross section ~ 11308 cm2, (approximately only 1/4 are open under normal pressure, so effective cross section is ~ 2827 cm2)
The sumtotal of cross-sections of venules followed by arterioles (~141 cm2) (venules more than arterioles as arterioles normally are under a tonal contraction)
Sumtotal of cross-sections of veins followed by arteries (~63 cm2)
Cross-section of Vena Cava ~ 1.38 cm2 followed by Aorta ~ 1.13 cm2

So if the cross sections are added up: Capillaries > Venules > Arterioles > Veins > Arteries

The Pressure Blood Pressure we measure is not exactly the flow pressure aka the pressure gradient. We measure the radial pressure not the pressure gradient. Special equipment is needed to measure pressure gradient.
The volume of fluid inside a parallel circuit (artery to capillary to vein) is not constant as plasma diffuses out at the small arterioles and capillary levels and diffuses back in at the venous side.
The pressure flow curve is not linear due to the compliance of the blood vessels.
The heart contributes very little to the blood flow in the veins. (To re emphasize that heart is not the only organ driving circulation). It is mainly through postural drainage and muscle action.

Coming to your question I like to point out one thing:
If there is a need to increase perfusion, the vasoconstriction occurs at the venular side. The capillary pressure is responsible for perfusion.

$$P_c = \frac{(R_{post}/R_{pre}).P_a + P_v}{1 + (R_{post}/R_{pre})}$$
  Where P - pressure and the characters a, v and c denotes artery, vein and capillary
  resistance
Rpost - Post-capillary resistance
Rpre - Pre-capillary resistance

The equation and picture are taken from Boron and Boulpaep textbook of Medical Physiology, 2nd Edition, Chapter 19: Arteries and Viens.

When there is a need to increase the perfusion to an organ the post capillary pressure is raised by venoconstiction (or in the case of glomeruli of kidney constriction of efferent arterioles). As you can see from the above equation, such a rise will cause rise in the capillary pressure and increase the perfusion.
Otherwise vasoconstriction occurs to do exactly what you assumed would happen: to redirect blood flow. In fact this happens at several levels:

Vasoconstriction of periphery (limbs) occur in cold conditions which causes cyanosis (meaning the flow is so reduced that most oxygen is used up)
Vasoconstriction of Splanchnic vessels occur when muscles need more blood (during exercise, flight, fight, etc...)

If you can read this chapter you will understand the equation much better. This book explains the physics behind physiology in a beautiful manner.


text:
what is the integral of PAR radiation over total solar radiation
This paper say 48%: What is the maximum efficiency with which photosynthesis can convert solar energy into biomass? -Zhu 2008
Also why does Zhu use 740 nm at high end of PAR wavelength!
My calculation says 43% (also using 7440 nm)
Have you done this integral? What did you find

What paper?  Could you give a name and / or link, please?  Thanks!

Yes the paper is: What is the maximum efficiency with which photosynthesis can convert solar energy into biomass? (Zhu,2008)

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Comparing maintenance energy costs of plant biomass vs bacterial biomass
Im interested if anyone has an idea if this research has been done or how you would approach it.
What is the energetic maintenance cost of (e.g) 2kg of some given bacterial cells vs 2 kg of a plant (like soybean).
Bacteria have less DNA to maintain per cell, less organelles, they dont fight gravity (not sure if this one matters), and probably have less active transport mechanisms. I guess the amount of energy they need just to maintain their biomass is much lower than a plant.

I did find this paper:
It shows the values normalized to nitrogen content prokaryotes ~150W/kgN vs plants 200 to 400W/kg N. But the study seem oh so complicated to me https://www.pnas.org/content/105/44/16994#T1

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Does sex-chromosomes exist in all the cells in a human body?
Each cell of a human body contains 46 chromosomes. So every cell must contain a pair of sex-chromosome. Is it true? Then a cell of a male and a cell of a female are always different and never be the same?

Like the other answer already said: yes, all cells in the human body contain all 2x 23 chromosomes (with the exception of cells that loose all nuclear DNA during maturation, like red blood cells, or cell produces by meiosis, which contain only a single set of 1x 23 chromosomes).
However, the more interesting part of your question remains to be answered:

Then a cell of a male and a cell of a female are always different and never be the same?

Technically it is true, that cells from a male and female can never be the same, however that difference is vanishingly small.
Genetically the difference is that female cells have two X chromosomes and male cells have one X and one Y. However:

in all female cells one of the two X chromosomes is permanently silenced (turned off), so essentially they also have only one (active) X chromosome.
the male exclusive Y chromosome is tiny. Size wise it is ~1% of the human genome, but it only has ~200 genes (of which only a portion is protein coding), which is even below 1% of all human genes (there are ~25.000 protein coding genes, around twice that much in total). Many of these genes are also only used/active in male exclusive organs.

These two points taken together mean that the majority of male and female cells do actually have the same active genes - and are therefore "the same" (there are of course many many other factors in biology, including individual differences, that require putting this into quotes).

+1 for recognizing that red blood cells are not the only cells that extrude their nucleus on maturation

All cells except mature rbcs contain genetic material. So every cell must contain 46 chromosome containing sex chromosome as well

Please provide a citation or link in reference to support for your answer. Thanks.

Yes, all cells except mature RBC have all the 23 pairs(22 autosomes + XX/XY) but due to different regulation mechanisms and deactivation due to heterochromatin, only the part of DNA actually useful to that particular cell type (like the gene for insulin in beta cells of pancreas) is used by it.
For Example: In the testis in the Leydig cells, only the androgen producing genes and other related genes are kept active.
https://en.wikipedia.org/wiki/Heterochromatin#Function
https://en.wikipedia.org/wiki/Regulation_of_gene_expression

Please provide a citation or link in reference to support for your answer. Thanks.


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Do primates have genetic predisposition to dominance hierarchies
I’m looking for some evidence to prove (or disprove) that primates are genetically predisposed to dominance hierarchies. I would appreciate any pointers/references to scientific literature.
PS:
The reason I am interested in this is as follows: primates (unlike many other less sophisticated animals) have a very little number of instincts. And yet certain types of behavior (for instance strong dominance hierarchies) seem to be a common case for some species; baboons, for example. And yet there are known cases of baboons (Sapolsky’s example) of a radical shift in social behavior towards less agressive and less dominance-based. This nevertheless looks rather as an exception and if so, raises the question if there indeed is a genetic predisposition to a certain behavior type.

This is one of those questions, where depending on how a person interprets the terms you use, one may give one answer or another. Hence it is difficult to answer.
You say that primates have very little number of instincts. And I react by: huh? Why would you say that? Then I realize it may depend on what you mean by instinct.
To the question on genetic predisposition. My reaction is: of course. Were you thinking of any other explanation? Which? But then I realize that it might depend on exactly what you mean by genetic predisposition.

And what kind of evidence might satisfy you? I very much doubt that know which primate alleles that affect dominance behavior. At least I doubt we know sufficiently much that it may be difficult to answer.

Eff, as an example: primates cannot swim (although as we know, humans can master it) while dogs, horses and plenty of other species have it encoded in them. So is a large number of other instincts. It regulates much less of primates behavior compared to other species. In terms of “what other explanation” could there be? Environment, as opposed to genetics. This also dictates the test criteria: genetically predisposed means validated across a broad array of environemntal conditions.

When something is 'genetic' and when something is 'environmental' is a difficult philosophical question. Do birds make nests because of the environment (availability of twigs etc) or because of their genes? What I would dare to say is that if the baboons had totally different genetics, then their behavior would most likely also be different. And for certain genomes, they most likely wouldn't engage in dominance behavior.

Also, just because something only happens in certain environments, that doesn't mean it wasn't genetic. You can easily imagine two species A and B, and two environments M and N. Species A might engage in dominance behavior in environment M, but not N. Species B does not engage in dominance behavior in either environment. This difference could be due to genetic differences, and yet the behavioral difference only manifests in environment M.


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Repopullation after a mass extinction
Is it possible to restart the whole human species with less than 10 individual.
let say that the whole human species was wipe out of the surface of the earth by a catastrophe only 8 different couple survive the catastrophe could they restart the human species?

The estimate is probably going to depend on the source, but it's generally at least an order of magnitude more than that.

Back in 2002, John Moore, an anthropologist at the University of Florida, calculated that a starship could leave Earth with 150 passengers on a 2000-year pilgrimage to another solar system, and upon arrival, the descendants of the original crew could colonize a new world there—as long as everyone was careful not to inbreed along the way. [...]
A starting population of 40,000 people maintains 100 percent of its variation, while the 10,000-person scenario stays relatively stable too. So, Smith concludes that a number between 10,000 and 40,000 is a pretty safe bet when it comes to preserving genetic variation.

For the general concept see minimum viable population.


text:
What does "crude" mean in this context?
Taken from Ian Freshney's Culture of Animal Cells:

The enzymes used most frequently for tissue disaggregation are
  crude preparations of trypsin, collagenase, elastase, pronase, Dispase, DNase, and hyaluronidase...

What does crude mean in this context?

In this context crude means naturally occurring or unrefined.
Purified trypsin alone, for example, is usually ineffective for tissue dissociation since it shows little selectivity for extracellular proteins.
Source: Worthington Tissue Dissociation Guide


text:
Why don't materials and methods describe culture media in volume?
After reading several materials and methods sections of cell culture experiments, I have not seen the recipe for culture media ever described in terms of volume.

Human adipose tissue was obtained from six samples of abdominal fat from female donors (age range: 20–45 years) after receiving informed consent and cultured as described in a previous study.[15] Briefly, samples were washed extensively with sterile phosphate-buffered saline (PBS) to remove contaminating debris and red blood cells. Washed aspirates were treated with 0.075% collagenase type I in PBS for 30 min at 37°C with gentle agitation. The collagenase I was inactivated with an equal volume of DMEM: F12/10% fetal bovine serum (FBS) and the infranatant centrifuged for 10 min at 800 rpm. The cellular pellet was resuspended in DMEM: F12/10% FBS and plated at 20000 cells/cm2 in T75 flasks in DMEM: F12 medium supplemented with 10% FBS and %1 Penicillin/streptomycin. After 24 h, it removed the nonadherent cells and expanded the adherent ADAS cells by serial passage. In this study, we used cells at passages 3–5 for all experiments and all experiments repeated at least in triplicate.

In this excerpt from the paper, Efficient transdifferentiation of human adipose-derived stem cells into Schwann-like cells: A promise for treatment of demyelinating diseases by Razavi et al, there is no mention of the volume of media used to culture the cells.
Moreover, there is no description of the height of the media in the dish, so it seems to me that from most cell culture descriptions, there is no way to properly reproduce the experiment simply by reading the paper.
Why do these sections fail to specify volume information?
Is there something that I'm missing here?

Have you checked reference 15?

@canadianer yes

The volume of media would be different for different culture vessels. You can check this site for the usual volumes. If they have not indicated then probably they used the usual culture volumes. You can check out their supplementary methods for more details on different experiments.


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TBX3 Protein structure and function
Is it possible for an anti-cancer monoclonal antibody to target the two repressor domains in the N and C terminal of the TBX3 protein ?

It is very unlikely that an antibody binds to two domains of a protein at the same time. If the two domains have a high structural similarity it might be possible that one TBX3 protein binds two identical antibodies. You could align the two domains and see if they have a common sequence stretch. If that's the case you could check if the stretch is unique, i.e. otherwise the antibody would bind to more than just RBX3.

Hypothetical questions have been asked here and we consider them on-topic if sufficient background and rationale is provided. Can you please elaborate your question? As it stands, it looks like a primarily opinion-based question and is likely to be put on-hold. Moreover, because of the lack of background, your question is also a bit unclear.


text:
Transformation of a multicellular organism
I was reading about using RNA-interference as a method of introducing pest-resistance in plants. In tobacco plants, using Agrobacterium vectors, genes specific to the nematode Meloidegyne incognitia were introduced. This was done in such a way that it produced both sense and anti-sense RNA in the host cell, forming dsRNA and ultimately silencing specific mRNA of the nematodes.
My question is, how can every single cell, or a proportion of cells sufficiently large so as to confer pest-resistance, of an already mature plant be transformed? Are a large number of vectors introduced, and as the infection gradually progresses, the immunity spreads throughout? Sorry if it's a stupid question, I've been out of touch with biology for a while.

Your inference is basically correct. The Agrobacterium acts as a vector for a plasmid containing the genetic construct one wishes to introduce into the plant genome. A medium containing a large number of bacterial cells transformed with this plasmid is injected into plant tissue, and the plasmids enter plant cells where parts of their DNA are integrated into the host genome. The overall effect of this is that there is localized integration in the areas where the Agrobacterium was introduced. A nice visual illustration of this comes from a paper from our lab where my colleagues introduced the genes for betalain biosynthesis into the tissue of Nicotiana benthamiana: in Figure 3 you will see only a localized area of cells around the injection site gain the ability to produce betalains.
You can find a nice review of the whole process of transformation with Agrobacterium here.


text:
How can a polar molecule pass through polar channels of proteins in the cell membrane?
To transport a polar molecule through the nonpolar cell membrane, a protein with a polar channel is needed to allow it to diffuse. However, if the molecule is polar and the channel is polar, wouldn't the molecule just be attracted to the polar amino acids and "stick" on the inside of it?
I may be thinking of this totally incorrectly, so please bear with my ignorance!
Thanks in advance :)

The water on both sides of the membrane is also polar. So that would help the transported molecule diffuse away from the protein once it passed through.

The molecule won't "stick" to the polar amino-acids for at least three reasons :

The amino-acids might not all be on the same plan, so their is always a force pulling the molecules transiting trough the channel in one direction (in or out the cell)
When  a flux is established, the repulsion forces between the molecules will force them to go in a direction, meaning that a coming molecule will basically push the ones already engaged in the channel.
For an ion or a protein, the water molecules constituting the hydratation shell of the molecule can't always follow it into the channel, so the water molecules present at the end of the channel (entry and end being relative to the direction of the flux) will more or less pull it outside the channel, as it is thermodynamically more stable to have a shell.  The fact that water molecules are able or not to follow the molecule depends on the size of the channel.

It's worth noting that water is itself a polar molecule, and that it can selectively cross the membrane thanks to channels called aquaporins.

Do you have a reference? Also, the first bullet point is hard to read. Perhaps explain the "molecules ", like, exported  particles or something. As of now it's quite unclear.

@AliceD : thank you for your remark, I clarified the first point.
Here can be found a reference relative to my third point.

No worries. +1 for the answer


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PBST vs. TBST buffer in western blotting
What is the advantages and disadvantages of using either PBST or TBST in western blotting, or while working with proteins in general? Are there other buffers which are also used for western blotting, or washing steps while working with proteins?

In my experience it actually doesn't matter which of these buffers are used for washing. I think this is much more a flavor of the respective lab.

I used to work for a company well-known for its modification state-specific antibodies, including phospho-specific ones, and they actually performed extensive in-house testing of PBST vs. TBST in Western blotting. Part of the reason the company chose to recommend the use of Tris-buffered saline over phosphate-buffered saline based buffers was the clearly-demonstrated fact that some phospho-specific antibodies just didn't work as well in PBST as they did in TBST, for whatever reason. As I recall (it's been quite a while since the testing was performed), some of the antibodies tested gave weaker signals, with more background, and one in particular just didn't work at all in PBST - no signal whatsoever. For that reason, the company chose to standardize its recommended Western blotting protocol with TBST, and it's been that way ever since.
That being said, I'm sure that the majority of antibodies out there would work just fine in either buffer. However, to be on the safe side, if a company states one buffer or other in their protocol, it would be best to use the recommended one.


text:
Measuring protein concentration, Bradford vs. Nanodrop?
I know that the bradford assay is a very standard way of measuring protein concentration after e.g. a purification. However, in the lab that I work in now they normally only use nano drop at the 280nm wavelength.
How trustworthy is this concentration? Say that I e.g. get 2.5 mg/mL, could I really trust this?

That depends strongly on your protein and how exact you need this concentration. Both tests (Bradford and the measurement at 280nm) only do an approximation.
The measurement at 280nm relies on the interaction of aromatic aminoacids with the UV light. If you have a protein with few or no aromatic amino acids, your measurement will be wrong.
The same is true for the Bradford assay. Here you form a complex between Coomassie Brilliant Blue and unpolar and cationic side chains of the amino acids. This test is more precise, since it includes more possible side chains, but is still dependend on the composition of the protein.
More precise is the BCA assay, since it utilizes the reduction of copper ions by the peptide bond of the protein.
What you could do is run a BCA assay (or at least a Bradford assay) from your sample and measure the same sample on the Nanodrop at 280nm and compare the results.
You can find an overview over the methods here and here.

I will aks the same as i did on Joe Boyle's answer, based on his common on extinction coefficient: when using the extinction coefficient for the protein in Nanodrop, how does it then compare to other methods? Does it then get more reliable

@CuriousTree knowing the exact epsilon value for a particular protein helps, but you're still stuck with the basic limitation of UV-based measurements - it entirely depends on the number of aromatic amino acids. The thing to keep in mind for any kind of quantitation assay is that you need to have a relevant standard. Not every protein is the same as, or even similar to BSA.

@CuriousTree When you know your protein very well, it might help, but in the moment you are analyzing protein mixtures (or something complex like cell lysates), this will not help.

The nanodrop should have an option that allows you to input an "extinction coefficient". This is a measurement of how much one mole of your protein will absorb at 280nm. The nanodrop will use this value to give you an accurate concentration reading.
To find the extinction coefficient for your protein, put its whole sequence into this server http://web.expasy.org/protparam/.
A few tips:

Use the exact buffer your protein is in as a blank.
Repeat your nanodrop reading a few times using a new pipette tip each time to ensure reproducibility
The purer your protein the more accurate your concentration reading will be! If there is a major contaminant in there, you will not get an accurate concentration reading.

thanks! Do you think this is comparable to Bradford then? because its specific for the protein?

Neither technique is perfect but they can both give good estimates. Bradford depends on your protein interacting with the Bradford reagent in a similar way to the known standard, unfortunately I don't have much experience using it.
If you need a precise concentration and have the time/resources then quantitative amino acid analysis would be my suggestion: link

@JoeBoyle if my peptide has no/few aromatic residues and I still want to use Nanodrop, will the use of  Expasy Protparam extinction coefficient input for Nanodrop become accurate enough?

@scamander If your protein has no aromatics you won't be able to use 280nm absorbance but if it has a low number you can still use the extinction coefficient. As usual, the quality of the reading will depend on how pure your protein is.

@JoeBoyle Thanks so much for your answer. Mine is a peptide (comes in powder).
How do you measure protein purity?

If you are dealing with a pure protein where there is nothing else present that will absorb at 280nm and if the E(1%, 280) of the pure protein is known or  may be calculated from the amino acid sequence, then A-280 measurement is a very accurate, fast, nondestructive method of determining protein concentration.
It is certainly much more reliable than any method that uses a standard curve, where the color produced may depend on the standard protein used.
It also has the additional advantage that the protein may be fully recovered after the measurement is made, often a consideration when dealing with precious samples.
It must be emphasized that the protein needs to be pure for this method to work.  When dealing with impure protein samples, the 'rule of thumb' is that a 1mg/ml solution will have an A-280 of 1, or E(0.1%, 280) = 1. But of course other substances such as DNA or toluene (in a yeast extract, maybe) may absorb at 280nm and play havoc with your readings.
A-280 measurements, being nondestructive, are usually considered adequate for monitoring eluates from chromatographic columns.
If the amino acid sequence is known and you wish to use the Perkins (1986) method to calculate the E(1%, 280) it is probably worth bearing in mind that this method takes no account of a bound prosthetic group (such as haem or tightly bound NAD), which could also significantly contribute E(1%, 280) value.
Some good refs
Perkins, S. J. (1986). Protein volumes and hydration effects. The calculation of partial specific volumes, neutron scattering matchpoints and 280-nm absorption coefficients for proteins and glycoproteins from amino acid sequences.  Eur. J. Biochem. 157, 169 - 180. [Pubmed]  [pdf]
Gill, S. C. & von Hippel, P. H. (1989). Calculation of protein extinction coefficients from amino acid sequence data.  Anal. Biochem. 182, 319 - 326.  [published erratum appears in Anal. Biochem. (1990) 189, 283].
Sober, E. K. & Sober, H. A. (1970). Molar extinction coefficients and E (1%, 280) values for proteins at selected wavelengths of the ultraviolet and visible region.  In Handbook of Biochemistry. Selected Data for Molecular Biology, 2nd edn.  Sober, H. A., Ed. pp C-71 - C-98. The Chemical Rubber Company, Cleveland, Ohio.
Edit
I can give an example of the Perkins method, if anyone is interested.

Best answer for purified proteins. With 280nm absorbance you can calculate a reasonably correct extinction coefficient from your sequence and then make a quick measurement on your nanodrop (using the UV module, not the protein module). This is more accurate than Bradford where you have a sequence-dependent error that you cannot correct for. Strictly speaking it is only valid for the unfolded state. You can measure in 6M Guanidinium chloride to be sure. In my experience, this is usually not necessary though and the value is pretty close for folded proteins, too.

The choice between colorimetric and direct quantification at A280 depends on both the protein to be quantified and the buffer being used. Generally A280 works well when you have a purified protein solution and the protein is well characterised. Entering the correct extinction coefficient will improve the accuracy of the concentration calculation. If using A280 it is also worth checking that your buffer does not absorb highly in the 280nm range. You can do this by blanking with water and running your buffer as a sample. If your buffer absorbs highly then you may be better off selecting another method.
For cell lysates and uncharacterised proteins you are better off with a colorimetric assay such as Bradford, BCA or Pierce 660. These can be run in microvolume but take care in the preparation, especially with assays such as Bradford that may have a lot of particulates.
Also, as you are measuring against a standard curve for colorimetric assays, the more similar your standards are to your sample, the better the results.
Andy


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What is overdiagnosis?
What is overdiagnosis ?
I have searched this Wiki result but didn't understood at all.
Can you please explain the first two line of Wikipedia :

Overdiagnosis is the diagnosis of "disease" that will never cause symptoms or death during a patient's lifetime. Overdiagnosis is a side effect of screening for early forms of disease.

Also

What is over treatment ?
Are overdiagnosis and over treatment same or different ?

@dustin, You can't ping a person if the person is not involved anywhere in the question/comments. You must ping Anne somewhere where she has either answered or commented

There is a good video of a conference dealing with this issue. Take a look if you are interested.

Overdiagnosis and overtreatment are intertwined. There is debate about how to best describe the problem, but narrowly defined, overdiagnosis occurs when increasingly sensitive tests - or changing definitions - identify abnormalities that are minor, non-progressive, or likely to resolve on their own, and that, if left untreated, will not cause symptoms or shorten an individual's life. Having a diagnosis makes well-persons think they're ill (overdiagnosis). If they are then treated for this diagnosis, they are overtreated.
An example involving changing definitions pertains to diabetes. When the official definition of diabetes changed from having a fasting blood sugar (FBS) of "X" or greater to an FBS of "X-y" or greater, 1.6 million new diabetics were instantly diagnosed, some of whom are not likely to develop symptoms and complications and are not likely to benefit from treatment. This is overdiagnosis.
If one goes on to put such a patient (let's say, on the lower end, "X-y+1" on a blood sugar (BS) lowering agent, and they pass out because their BS drops too low, then they are overtreated. If they happened to be driving when they pass out, and get into a fatal accident, they literally die from overtreatment, if it can't be shown that they would have suffered from a marginally elevated FBS. (If it can be shown to be dangerous to have an FBS of X-y+1, then this is a risk of treatment, not overtreatment.)
For an example of increased sensitivity of tests, say a new test is available, a blood test called a "D-dimer", which will reveal with 100% accuracy the presence of a dangerous pulmonary embolism (it's very sensitive). However, it is also known to be positive when there is no pulmonary embolism as well, but it's not known how often (so it's not specific). But it's an exciting new test!
A patient goes into the Emergency room for one of the following: atypical chest pain, dizziness, shortness of breath, leg pain consistent with a blood clot in the calf, or loss of consciousness. In addition to an EKG, chest x-ray (CXR) and a few other tests, a D-dimer is ordered. The EKG, CXR and other tests are negative, but the D-Dimer is positive. The tentative diagnosis is pulmonary embolism (PE).
Because the D-dimer indicates that a dangerous condition may be present, a spiral CAT Scan with contrast is ordered on all those people. Some will have a life-threatening PE (appropriately diagnosed*). A large number will have a negative CAT Scan. (diagnosis excluded) But a significant number will have a very small PE. Because this is relatively new and surprising, and it's not known whether they should be treated (maybe nothing will happen if they don't treat? Maybe this happens in normal people and we just never knew it?), the doctors, who are accustomed to treating all PE's will put the patients on blood thinners. This is overdiagnosis of PE, and treating it is overtreatment, because some treated people will have "bleeds" - a stroke, GI bleeding, other. It is now known that these tiny PE's are often seen in patients who suffer no harm at all from them, therefore in order to stem overdiagnosis (and subsequent overtreatment), the D-dimer test is ordered less frequently.

...[We] are in the midst of an epidemic of diagnosis. Conventional wisdom tells us that finding problems early saves lives because we have the opportunity to fix the problems early. [Conventional wisdom tells us that} There is no risk in finding things early. The truth is that early diagnosis is a double-edged sword; while it has the potential to help some, it has a potential to harm us. Such overdiagnosis leads to overtreatment when these “pseudo-diseases” are conventionally managed and treated as if they were real abnormalities; because these findings have a benign prognosis, treatment can only do harm.

Overdiagnosed: Making People Sick in the Pursuit of Health
Overdiagnosis
Using Evidence to Combat Overdiagnosis and Overtreatment: Evaluating Treatments, Tests, and Disease Definitions in the Time of Too Much

Are all overtreatments due to overdiagnosis? If yes, please mention it explicitly. If no, please make a distinction.

As with most things, it depends on your definition. If you define overtreatment as the result of overdiagnosis, as most do, then yes. If someone treats a medical condition which needs to be treated, but with more medicine than needed to control it, that is considered overaggressive treatment. If you define overaggressive at overtreatment (which confuses the issue which is very much discussed and written about), then you're correct. But in light of the issue, I would avoid that definition.

Thanks for clarifying. But overaggressive treatment is generally not considered overtreatment? Or is the definition not properly set yet (meaning no standard definition?)

Screening is the process of testing the population enmasse to check for the presence of risk factors for a disease or to detect the early form of a disease.

Usually the tests that are used in screening are not highly effective in excluding people who do not have the disease (low negative predictive value). Instead the goal of screening is to identify as many people as possible (high positive predictive value) who may have "the disease" which is being screened.
When screening for early form of disease, people who may never develop the disease in their lifetimes are also detected and they may be treated without the actual need. In such cases the treatment will result in more harm than the disease itself.

Usually after screening, people who are recognised to have the risk factors are subjected to further confirmatory tests which will then exclude the people who do not have the disease.
Overdiagnosis is said to be done when a lot of people who don't have the disease at the present time are treated for the disease just because they have the risk factors for getting the disease or have the early form.
Overtreatment is not the same as overdiagnosis. Overtreatment refers to treating a disease more vigorously than warranted. The main difference is that in overtreatment, the treatment is provided for even correctly diagnosed disease but excessively. This may include unneeded medical procedures, injections etc...
For example getting antibiotics for a common cold (with just running nose) which has lasted for less than one week may be considered overtreatment.
Overdiagnosis may lead to overtreatment. However all overtreatment is not due to overdiagnosis.
Edit:
I have edited the answer thanks to anongoodnurse.

An X-ray is not a treatment. It can't be included with overtreatment, nor is a chest ray alone without findings ever part of overdiagnosis. That would be a negative CXR. Treating a newly diagnosed disease in it's early form may be very beneficial, e.g. with Multiple Sclerosis. That is not overdiagnosis or overtreatment. You've got a few things confused here. I don't know if this is because you over-rely on Wikipedia or not, but I think it may have something to do with it.

I have written nothing about chest xray and overdiagnosis. Are not redundant medical procedures considered overtreatment? Now that you said that unnecessary diagnostic procedures can't be considered overtreatment - what would they be called? (I am genuinely interested in knowing and not asking for the sake of arguement (which seem to set the tone between us in most of our conversations! Lol)) @anongoodnurse

"For example getting a X-ray for a common cold which has lasted for less than one week may be considered overtreatment." I assumed you meant a CXR? What other XRay is commonly obtained for a URI?

Yes, I meant chest x-ray but I did not mean that it was overdiagnosis. I did not mean to say that getting a chest x-ray was overdiagnosis. Just that it is unwarranted in such a case therefore unnecessary medical procedure - which (I thought) was overtreatment @anongoodnurse - This idea was corrected thanks to you. But I am interested in knowing what you call such unnecessary medical procedures


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How common are the "common" human coronaviruses?
I was listening to a virology expert on the Swedish radio yesterday. He said that there already were several corona viruses among humans that only affected children because basically all the adults were already immune. He said that he believed that SARS-CoV-2 will be added to this category in the future, which seemed logical to me. Basically SARS-CoV-2 will at some future time only affect children and give very little symptoms because all the adults will be immune.
By googling I found four viruses listed as "common corona viruses" that affects humans:
229E (alpha coronavirus)
NL63 (alpha coronavirus)
OC43 (beta coronavirus)
HKU1 (beta coronavirus)
1.Can something be said about how "common" these viruses are?
2.I mean if an adult for some reason has no immunity to one of these viruses how long will it take on average before he gets infected?
The reason I am asking is because if we know the answer to question 2 above for the four common coronaviruses one maybe can produce an educated guess for the likelihood for a person escaping the "first wave" of SARS-CoV-2 getting infected within a given time period after we have "herd immunity" against SARS-CoV-2.

I'd question pretty much anything else that "virology expert" says, since they seem to be well outside the mainstream understanding of these viruses.

It was this guy: https://liu.se/en/employee/lensv66 Maybe people invited to public radio fell that their role is to calm the public rather than to be totally accurate.

The common [cold] coronaviruses are pretty common:

Four HCoVs (HCoV 229E, NL63, OC43, and HKU1) are endemic globally and account for 10% to 30% of upper respiratory tract infections in adults.

To pick a more detailed study in Ghana:

This study sought to determine whether human coronaviruses (HCoVs) are associated with upper respiratory tract infections among older children and adults in Ghana. We conducted a case control study among older children and adults in three rural areas of Ghana using asymptomatic subjects as controls. [...]
Out of 1,213 subjects recruited, 150 (12.4%) were positive for one or more viruses. Of these, single virus detections occurred in 146 subjects (12.0%) and multiple detections occurred in 4 (0.3%). Compared with control subjects, infections with HCoV-229E (OR = 5.15, 95%CI = 2.24–11.78), HCoV-OC43 (OR = 6.16, 95%CI = 1.77–21.65) and combine HCoVs (OR = 2.36, 95%CI = 1.5 = 3.72) were associated with upper respiratory tract infections. HCoVs were found to be seasonally dependent with significant detections in the harmattan season (mainly HCoV-229E) and wet season (mainly HCoV-NL63).

Occasionally there are substantial outbreaks of common cold, e.g. as observed in Japan:

we conducted a longitudinal survey
between 2010 and 2013 in Yamagata, Japan, to clarify
the epidemiology of HCoVs using RT-PCR methods
[...]. In 2011, we
found that the monthly detection frequencies of HCoVNL63 were higher than 20% in January and February
(28.5% and 25.3%, respectively), whereas those of the
other HCoVs (HCoV-229E, -OC43, -HKU1) did not exceed 20%. In light of these findings, we continued
the HCoV surveillance and, thus, captured data from
the largest outbreak of HCoV-OC43 reported in the last
6 years. During the 2014–2015 influenza season in
Yamagata, Japan, the monthly detection frequencies
were approximately 30–40%.

Those percentages are from people reporting symptoms (and then swabbed.) The graph below (from the same paper) nicely shows the seasonality.

Monthly distribution of clinical specimens (A) and HCoVs (B) detected from patients with acute respiratory
infections between January 2014 and March 2015, in Yamagata, Japan.

Question 2 is rather meaningless because immunity to common coronaviruses is short lived. See (also) this answer (esp. the 2nd table) to a related question putting the common coronaviruses immunity duration in perspective; reproducing just the table below (the relevant line for common coronavirus is the 1st below the break, i.e. 1st in the 2nd section of the table).

And I've managed to track down one of the primary studies on 229E long-term immunity (or rather lack thereof)

Although after 1 year concentrations of specific serum IgG and nasal IgA were
still significantly raised in the infected group, they were much lower than at the
maximum. [...] When challenged after 1 year all of the original uninfected group were infected and 6/9 of the infected group were reinfected. [...] In the infected group there were considerable individual differences. Some lost their antibody, particularly serum antibody, completely by 1 year, some did not.

And it's basically impossible not be exposed to a strain of the common cold coronaviruses at one point; one study on newborns found that interval to be 3.5 years, but that's probably an overestimation for adults.

all of the children had maternal anti-NL63 and anti-229E antibodies at birth that disappeared within 3 months [...] on average, HCoV-NL63 and HCoV-229E seroconversion occurs before children reach the age of 3.5 years.

The real question is whether Covid-19 will behave like the common coronaviruses or more like SARS and MERS for which it is suspected (from the detection of antibodies), but not certain that immunity lasts longer.

For the SARS and MERS coronaviruses, antibodies appear to persist for several years, but no studies have intentionally attempted to re-infect people, since these are deadly diseases.

Persistence of antibody isn't a direct measure of immunity; Memory B cells remain and can mount an immune response after circulating antibodies are gone.


text:
Why do archaea survive better in extremes than bacteria?
Why have bacteria not evolved to fill the extreme environments to the same extent as archaea?
What has enabled archaea to colonize these areas when bacteria do not?

Many bacterial phyla are thermophilic: Thermotoga, Geobacillus, Thermus, Deinococcus are some examples of note. There are many factors, such as S-layer coating, polyamines, thermostable enzymes, all well documented: please rephrase with specific aspect you are struggling to find. Thanks!

I suspect this falls under the no-homework policy, so I will not give a full answer, just lots of links to point in the right direction. A good reading material is the genome sequence papers, such as that for Methanopyrus kalderi.
The domain Archaea contains some of the most thermophilic organisms of this planet. Very thermophilic organisms are called hypethermophiles, but employ very much the same strategies.
Thermophilic bacteria
However, not all thermophiles are archaea, some notable bacteria phyla that are thermophilic are Thermotogae, Aquificae, Thermus-Deinococcus clade and some phyla have several thermophilic genera, such a Firmicutes with Geobacillus. Taq polymerase for PCR comes from Thermus aquaticus (its relative Deinococcus radidurans was nicknamed Conan the bacterium due to its radiation resistance, so is notable for other reasons), Thermotoga maritima was a subject of a structural genomics screen and is highly studied and Geobacillus is a treasure trove for biotech (see PubMed).
HGT
These bacteria share many genes with archaea by HGT.Thermotoga maritima shares 24% of its genes with archaea. So it is best to talk about thermophilicity in general.
Mesophilic archaea
Not all archaea are thermophilic. The methanogens, such as Methanobrevibacter, are mesophilic and actually a lot of research, such as vaccine and methane pathway antimetabolite development is ongoing.
Shell
Firstly, the cells do not need to burst. To do so they employ a shield of protein that pack in a crystalline lattice called the S-layer. Geobacillus a firmicute (i.e. monoderm with thick peptidoglycan) has it too despite the peptidoglycan.
Firmicute spores are annoyingly resistant as they contain dipicolinate. Geobacillus expecially so.
DNA
Secondly, the DNA must not denature. Archaea have high GC content, but the thermophilic bacteria generally don't, hence why biotech likes the latter more. A key feature is high levels of polyamines, which stabilise the phosphate groups.
Lipids
Archaea, but not bacteria, have a unique membrane composition, which is reviewed here.
Protein
Every protein has a melting point. The more contact it has the more stable it gets. These often require expensive to make amino acids. There are many analyses of amino acid composition of thermophiles in PubMed, but be warned that some papers suffer from bias from archaeal high GC.
Enzymes
Now, a thing to note is that an thermophile will do poorly at a lower one. This is because of enzyme kinetics and temperature dependence. Namely, the kcat and (less so) the kon and koff of the MM change with the Arrhenius equation in the transition state theory. In a more accurate model, it follows the Eyring equation. In actuality is even more complicated (and fascinating) and explained with the Macromolecular rate theory (and here) where the fluidity of the 3D structure of the protein plays a part. But in short, turnover (k_cat) and Michaelis constant (K_M) go up with temperature, while the former is good (faster), the latter is bad as it needs to be close to physiological substrate concentration. Going down in temperature, the enzyme will be slower, but will find its substrate.


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How do scientists kill the bacteria they themselves made resistant?
I was reading this article on researching bacteria resistance to silver by removing some of their genes.

Researchers then used "colony-scoring" software to measure the differences in growth and size of each plate's bacterial colony. E. coli strains with genes deleted involved in producing sensitivity, or toxicity, to silver grew larger colonies. Strains with genes deleted involved with resistance grew smaller colonies.

Once you end up with some resistant bacteria and you're done researching it, you can't just flush it down the toilet. How do you safely dispose those colony plates in a way that ensures those bacteria don't get out into the wild and reproduce?

The problem with your search is the word "remove". That's not how we normally describe sterilizing, decontaminating, or cleaning biohazards or killing bacteria, or "safely dispose".  https://www.google.com/search?q=how+do+scientists+sterilize+bacteria+after+experiment  got google to suggest "How do you sterilize a petri dish?" for example.

You are absolutely right, flushing down the toilet (or the sink) or simply throwing them into the normal waste doesn't work for biosafety reasons. And it is also not allowed, depending on the country you would do this in, this can lead to hefty fines.
Biologically contaminated lab waste can be inactivated (=all potential dangerous organisms are destroyed) by two ways: Either by heat or chemically. Which ways is used, depends on the kind of waste.
The most commonly used way is autoclaving, meaning treating the waste with steam at high temperatures at higher pressure. The temperature used here is usually 121°C, the exposure time depends on the volume of the waste, since the temperature needs to be reached and kept for at least 20 minutes. See the references for more details.
Liquid wastes (like culture media) can also be inactivated chemically by adding chlorine bleach to decompose the cells. Bleach can also be used to decontaminate surfaces, although here more often alcoholic solutions (70% Ethanol or Isopropanol) are used. After chemical inactivation, the remaining solutions should not be autoclaved as the emerging fumes are either unhealthy (bleach) or explosive (alcoholic solutions) and this is unnecessary, too.
Liquid wastes can also be autoclaved to inactivate them.
Autoclaving has the main advantage that it is rather simple (put the waste into the autoclave, close it and run a appropriate program), the waste can afterwards simply be discarded as normal waste, which may not be the case for chemically inactivated waste, which may need special precaution for disposal.
References:

Decontamination and Sterilization
Decontamination of laboratory microbiological waste by steam
sterilization.
TECHNIQUES FOR STEAM STERILIZING LABORATORY WASTE
Decontamination of Laboratory Microbiological Wasteby Steam Sterilization

I think the important concept is that they're not really invulnerable like Superman, just that anything that would kill them would also kill a patient infected with them. You can incinerate a petri dish, but not a person.

@Barmar Technically you can, just not a person you want to stay alive. ;)

Obligatory XKCD.  (The point, in case it wasn't clear, is that killing bacteria, even resistant bacteria, is really easy.  The problem is that all the best treatments tend to kill humans too, so they're difficult to apply safely.

There is a third method, rarely used:  gamma irradiation.  You need quite a setup to safely handle this, but it has the advantage that it kills the target without utterly destroying it--useful when you're dealing with BSL-4 stuff as many things can still be learned without the risk of the real thing.

Do NOT bleach the organism and then autoclave it.

@xyz123 Good point, I added it to the answer.

Dumb question because I'm not a biologist: would freezing work too? Why does it have to be heat or chemical means? (I do realize that some bacteria can survive low temperatures though).

@EJoshuaS-ReinstateMonica Because freezing is a good way to actually preserve bacteria. This is routinely done in the lab to make stocks of bacteria you want to keep. Heat/chemicals destroy the structural integrity of the bacteria or at least of important parts of them.

@EJoshuaS-ReinstateMonica You need to break the cell membrane or the organelles of the bacteria for it to be dead. Freezing doesn't break anything apart, it just pushes it further together. Adding heat will lead to expansion or burning or some other chemical reaction (like proteins breaking apart), all of which will usually kill living things. Also, since bacteria are also basically animal cells, you can think of it like cooking or freezing meat. Freezing preserves the meat and cooking will lead to various chemical changes.

@JohnHamilton and Christ - thanks, good points. (In case it's not obvious, I'm not a biologist, hence my dumb question :) ).

@EJoshuaS-ReinstateMonica That's what I assumed, but this is fine. Stackexchange is about asking questions and have them answered :-)

@EJoshuaS-ReinstateMonica "It is not shameful to not know, it is only shameful to not learn." It may not be an exact translation but this is my favorite quote from Ataturk. So, ask away, even if the question seems dumb to you, if you're learning, it's all good.

To address what seems to be the misconception underlying your question:
Killing pathogenic bacteria is not difficult; killing them without harming their (usually human) host is.
This is why antibiotics are so precious:
They are drugs that affect only bacteria¹ – by exploiting properties that are unique to them.
It is usually resistance to antibiotics that we care about in bacteria, because it makes infections with such bacteria more difficult or even impossible to treat.
Once we investigate bacteria in vitro, e.g., in a Petri dish, there is no host that has to survive and thus we have far more options to kill them.
The other answers have listed plenty of methods to do this – which are all lethal to humans as well.

¹ This is of course somewhat simplified: Every drug has a side effect, and so do antibiotics. But their side effects on humans are more lenient than their primary effect on bacteria.

Resistance Is...Reversible?
While people generally don't talk about bacteria losing antibiotic resistance, it does happen, and for a pretty obvious reason: the biochemical tools which confer resistance come at a metabolic/reliability/efficiency cost, or the bacteria would have had the resistance to begin with.  In general, we can assume that bacteria are not adept at dealing with silver toxicity because silver does not occur often enough in their favorite environments.  When you take the bacteria out of a silver-concentrated environment, there is no longer pressure to take extra measures to deal with it, and the resistance can be lost.
A Pound of Flesh
There are many ways to attack microbes, and even more ways for them to respond.  The CDC provides a nice overview of some strategies.
Take fluoroquinolones, for instance.  They kill bacteria by suppressing the enzymes which uncoil DNA.  As you can imagine, this makes for a Very Bad DayTM for the bacteria.  If you're a bacterium, and you end up with some ciproflaxin inside your membrane, the most obvious thing to do is get rid of it.  Some bacteria, like P. aeruginosa, which are resistant to ciproflaxin do just that: they build pumps in their membranes to pump it out.  But as any engineer will tell you, adding new pumps to a system costs both space and energy which could have been used for other things (like finding food, reproducing, etc.), so you wouldn't do this unless you absolutely had to.
How do we know that they actually lose resistance?  Well, we've observed it happening!  We literally know which mutations and gene transfers are necessary to confer various resistances for P. aeruginosa, because wild strains are both resistant and susceptible, depending on their exposure to antibiotics (or laboratory conditions).
Gray Goo
Be glad that biology tends to find the most efficient solutions.  This energy minimization tendency might be characterized as a kind of laziness, but it's really an optimal strategy for allocating your energy where it gives you the most value.  For a microbe, that would be finding food and reproducing.  That means that once the lab-grown freaks escape into the wild, whatever super-powers they gained from our mad scientist experiments are likely to be lost over time, once we stop bathing them in mutagenic toxins.
Unlike nanotechnology-gone-wild, we actually don't have so much to fear from lab-induced antibiotic resistance.  It is the pernicious and casual use of antibiotics in our daily lives that will kill us in the end.  These flow down our drains and into our streams and rivers and evolve those critters night and day, virtually guaranteeing that we will encounter resistant types in the wild.

Interesting answer, but it does not answer the question.

While it doesn't answer the question as asked I think this answer provides important background (+1):  that resistance often does come at a cost for the bacteria and thus resistant bacteria are at a disadvantage compared to "wild-type" when the antibiotic pressure is gone again. (This may look different for induced resistance: induced resistance means that the resistance mechanism/pathway is only expressed if needed)

For a species to completely evolve away from resistance, the resistant ones have to die off. So you need some way of killing resistant bacteria to begin with.

@Chris It was a frame challenge.  OP said "you can't just flush it down the toilet", and I attempted to describe why that's not actually a catastrophic outcome. I think your answer covered the conventional sterilization techniques quite well, so I wanted to offer another perspective.

@Acccumulation Time will do that just fine. No bacterium are observed to be immortal (though certain tumors might be). With each generation (on the order of hours, for many genotypes), the ones which don't carry around the unnecessary weight of resistance mechanisms will slowly gain ground on those that do, via mutation, horizontal gene transfer, etc.

@LawnmowerMan While I agree with cbeleites that there is some useful background in this answer, I don't think the frame challenge is all that useful. "You can't just flush it down the toilet" is not merely an assertion of the OP but a common safety standard imposed by legal and regulatory codes, even for fairly low-risk applications. Although I fully agree with you that casual antibiotic use is far more dangerous than lab-grown resistance introduced to low-risk model organisms, practically we don't permit those lower risks to go unabated.

Resistant to WHAT?
Scientists generally deal with bacteria resistant to some concentration of some particular substance (or combination thereof).
Those strains are still pretty much sensitive to great deal of other substances (e.g. etanol 70%), high temperature (boiling water at normal pressure or higher), etc generic ways to kill bacteria.

Autoclave at 120 degrees Celsius for 30 minutes. [ref]
Don't ever flush biological material, living animals, or anything other than sanitary-code approved waste down the toilet.
The proper way to dispose of used culture material is to sterelize it first, then dispose in sealed bags.

After counting, petri dishes should be secured in a plastic autoclave
  bag and autoclaved prior to disposal.  During multi-day field trips,
  place used petri dishes in plastic autoclave bags, and close the bags
  for transport to the office.  Then, following autoclaving, place the
  closed bags of petri dishes in dumpsters or other containers that will
  be emptied mechanically, to prevent accidental contact with people or
  animals.  Never place petri dishes in motel or office wastebaskets.

On a more budget-restricted level, when I worked in a high school, the science lab tech would take all the old Petri dishes out of a dedicated disposals freezer, and take them to the campus coal fired boiler.
Since the boiler only ran in Winter, there was a lot of stuff to dispose in the first few cold days in Autumn.  As such, the science department scheduled much of this work over winter.   Work involving dissection also produced a lot of biowaste, but that was less-bad and could be disposed of in the general waste (it was the 80s, not a lot of recycling at the time.)
Once the furnace part of the boiler was at temperature, the thing was shuttered (somehow) and the access hatch opened.  The frozen plastic dishes were thrown in, inside either paper or plastic shopping bags for ease of handling, then the hatch was closed and the dampers opened.
As for PPE, it wasn't much of a thing.  Disposable gloves were worn for handling the dishes, and they went into the furnace once the dishes were all gone.
I remember once looking in the furnace when it was cold, before the ashes were raked out.  There was zero trace of any material left behind, even metal items like staples or clips were vapourised.
In short - Burnination


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Where do methyl groups in the human body come from?
Where do methyl groups in the human body or other mammals come from? Do we synthesize them (where?) Do we get them from our diets (in what? anything beside methionine?) Do our gut microbes produce them for us (and are we dependent on them for that?)

Well, as it's Christmas, I'll play Santa and give you some S-adenosylmethionine for your biochemistry Lego set. You'll need to consult the instruction page to see how to use it and what other pieces are needed. Another time you may find the biochemistry manual useful for the research you are expected to do before posting.

Thank you for your response.  I am new here and did not see instructions about what I was supposed to do before posting a question.  Regarding the question itself: the methionine-homocysteine cycle does not CREATE methyl groups--it only passes them around and activates/deactivates them.  I am trying to find out where they are synthesized, whether we have endogenous production of them or are reliant on exogenous sources, and if so, what are those sources. (I find it hard to believe that we can get enough solely from ingestion of methionine.)  Anyone else?  Thanks.

Read the whole section. The methyl group for the cycle comes from methylene tetrahydrofolate, which is produced by the reaction of serine with tetrahydrofolate. And serine, as you should know from your studies of the central metabolic pathways, is not an essential amino acid, but is synthesized from an intermediate of glycolysis. You wouldn't be thinking that methylation only happens to the amino acid residues of histones, or that you can understand its bichemistry without actually studying basic biochemistry, would you?


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Appropriate regeneration of StrepTrap HP columns for FPLC
My question is related to protein purification using a ÄKTA FPLC.
We used StrepTrap HP Columns (1 ml column Volume (CV)) from GE Healthcare Life Sciences to purify a strep-tagged protein. In the first approach, this worked pretty fine.
We wanted to re-use the columns after regenerating them according to the official protocol. The included steps were all performed at a flow rate of 1 ml/min and with filtered solutions:

3 CV distilled water
3 CV 0.5 M NaOH
3 CV distilled water
5 CV 20 % EtOH
Storage of columns in 20 % EtOH at 4°C.
Equilibration of the columns with Binding Buffer just before next use.

By adhering to the protocol we encountered some problems with the next purification (it was the same protein, but a new sample of cell extract). The purification worked less effective and the amount of purified protein was very low.
We tried a slightly different protocol for regeneration, also at a flow rate of 1 ml/min and filtered solutions.

5 CV distilled water
5 CV 20 % EtOH
3 CV 6 M Guanidinhydrochloride (sol.)
5 CV 0.5 M NaOH
3 CV distilled water
5 CV 20 % EtOH
Storage in 20 % EtOH at 4°C
Equilibration with Binding Buffer before next use.

We chose the Guanidinhydrochloride to denaturate all remaining proteins from the column resin and support the regeneration by this.
But also with this protocol we encountered the same problems (low efficiency of purification).
I would be very interested if anyone of you have encountered the same problems and maybe have a solution/better protocol for this regeneration step.
Thank you for your suggests in advance! :)

What was the exact problem with the second purification (eg poor binding, poor elution, etc). Did anything change with the preparation of the second sample? Did you use desthiobiotin for the first elution? Is there a lot of biotin in the culture medium?

We used desthiobiotin (2.5 mM in Binding Buffer (Tris, NaCl, EDTA)) as Elution buffer. The second sample was prepared exactly the same way as the one before (same incubation time, same induction of protein expression). Additionaly we tried it with another protein (with a new column) and observed the same problem. Meaning: First purification was rather good, the second was not so nice. The culture medium contained 0.2 g/l Biotin (CGXII+Glucose). What we observed during the FPLC was, that the peak for the eluted protein was not very high. We are not sure, if this is because of poor binding.

Or because of poor elution. We tested the flowthrough on an SDS-PAGE and it seems in both cases (the first attempt, where the purification was fine, and the one where it was not) that we have enough protein in the sample (strong bands at the expected MW of our protein in the cell extract and still in the flowthrough.).

How much of your target protein is in the flow through compared to the sample that was applied? That should tell you how well it is binding. You might want to think about how much of the biotin in the culture medium is making it to your column. Biotin will bind with very high affinity and prevent binding of the strep-tagged protein. It might be irrelevant but is perhaps worth considering.

Is there a technique to determine the amount of target protein in the cell extract and in the flow through? I guess a BCA Assay e.g. would just give you the amount of total protein in the sample? The remaining Biotin is a very good point I have not thought about at this point! Is a HABA assay an appropriate way to measure the Biotin amount in the sample?

I would just compare the bands on SDS-PAGE. You don’t really need to determine the exact amount that bound but rather just get a rough idea of whether it is binding at all.

HABA binds to streptavidin in the same site where biotin binds, so you could use it in combination with streptavidin to assay biotin concentration. That might be more trouble than it’s worth though. If you are worried about biotin blocking the column, you could instead use HABA to check the column for binding capacity.

You might try contacting customer support before you get too deep into troubleshooting yourself as they may have seen a lot of these problems and have solutions already.

Ah okay, we did this already. What you can observe is, that you have a rather strong band for the cell extract and also for the flow through (we chose a very high induction rate, which is tolerated by the organism). And also for the fraction, where the purified protein should be, you can see a very clear and strong band. We approved, that the protein is in all three samples by Western blotting, where you can see a very nice and clear signal for the purified fraction. This is only for the first attempt with a fresh column, the second run resulted in a much lower signal for the pur. protein.

Yes, I agree with you. The first approach before overextending the tests would be to ask customer support. I was just curious for some ideas or experiences with this problems. I will add it here, if there might be some useful input from the customer support! Thank you very much for your assumptions and ideas :)

There could be a couple of things affecting the binding capacity of the column, but prime suspects would be either damage to the strep-tactin proteins or some sort of irreversible binding occurring. I would contact support and give them all details of your experiment.

I'm starting to suspect we are having issues with the column regeneration too. Did customer support ever get back to you? I've not worked with StrepTraps before, but I'd expect the resin to last more than half a dozen purifications, so I'm working with we haven't managed to elute all the protein from previous runs and all the column is saturated meaning all new proteins flow straight through. It would be great if you could share how you fixed this! Thanks
Abbie


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How can the phenotypic effects of a tumor suppressor mutation be silenced?
I've been reading a little about the "two-hit" hypothesis for tumor suppressor genes here, which mentions that some genes exhibiting haploinsufficiency are exceptions to the hypothesis. I've read elsewhere on this site (namely the answer to this question) that suggests haplosufficiency as a means of "silencing" the mutation of the tumor suppressor gene such that the expression of the wild-type allele compensates for the mutant allele.
Are there any other mechanisms that contribute to incomplete penetrance of tumor suppressor mutations?

This is more of a comment

Mutation in tumour suppressor is a recessive trait and there is no active "silencing" of the mutation. If a tumour suppressor is a TF then a mutation in the DNA binding domain can have no effect if there is a complementary mutation in its binding site. This is just a theoretical possibility and I have not heard of any examples as such. I don't think any other mechanisms exist for "silencing" any loss of function mutation.


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To what exten do children produce antibodies against covid-19?
Here in Sweden all kindergartens and schools up to the month of June the year people turn 16 remain open. In almost all other European country schools are closed.
I do not really know why our schools are open, the official policy is unclear. One idea though is to get the children to catch the disease while the elders remain in hiding in order to acquire more immunity in the society.
However, according to some Chinese study younger people seem to be able to fight the disease without antibodies. In the age group 15-39 the number of antibodies found were less then a third of the number of antibodies found in the age group 60-85.
https://www.scmp.com/news/china/science/article/3078840/coronavirus-low-antibody-levels-raise-questions-about
Question: To what extent does infected people in the age group 0-16 develop antibodies against covid-19?
I know that presence of antibodies do not necessarily guarantee immunity against reinfection but if children do not produce enough antibodies they will obviously not be immune.

There are many levels in the word immune, children are mostly immune against the disease and their innate immune system has to do something with it. That said they often develop a benign infection and a question is if they are contagious (a single children probably not much, due to Chinese studies not finding any single case where contagion from a children was obvious, but as a population, in schools with many close contacts and poor hygiene it might be very different).

One report stated that closing schools only has a marginal effect. If they are not sneezing and coughing and putting snot in rags, it limits their viral output. people who don't even have a temperature don't have as high numbers of a virus as people who have flu symptoms. For antibodies, it seems that children's immune system does actively fight the virus very efficiently, and that would be with antibodies. studies will take a while.


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Zinc, zinc ionophores and viruses
I see that scientist are sometimes trying to use so called "zinc ionophores" to get human cells to take up more zinc. Zinc is believed to sometimes reduce the ability of viruses to replicate, maybe depending on what type of virus it is. Some zinc ionophores are readily available as dietary supplements. I am thinking first and foremost on quercetin and Epigallocatechin gallate (EGCG).

Is there any way to test how "open" ones zinc-channels into the cells are?
Is there any research done on how much a person typically would need to consume of a certain ionophore to get a descent amount of zinc in the cells?
Zinc tablets are available as dietary supplements. Is there any point in taking those if you want more zinc into your cells or is it more or less pointless if you are lacking ionophores?

SE Biology is concerned with the mechanisms of biological processes, not with medical or public health problems per se. Health advice is explicitly off-topic. Some general questions about coronavirus may be on-topic for our sister site, SE Medical Sciences, otherwise I suggest that you to consult an appropriate reputable sources for coronavirus information, some of which are listed here.

It is not pointless.  Some zinc will get in.  But only a small fraction of the zinc you take.  In the short term, relatively high doses of zinc (like twice the RDA) should be okay.  You could take them with green tea, which includes ionophores.