genetics - How are there multiple varieties of the potato?

Well, uvesten is correct in saying that potatoes are flowering plants and as such they can reproduce sexually. However, as everyone mentions potatoes can, like many plants, reproduce asexually by putting out clones.

Since clones are (by definition) genetically identical to the parent plant, this would seem to rule out the possibility of producing different varieties (or even species) from clonal propagation.

But! this very interesting study by Jiang et al. looked at Arabidopsis lineages (Brassica family). They found:

"in vitro regeneration of Arabidopsis plants results in a high frequency of heritable phenotypic variation "

That is, regenerant Arabidopsis plant lineages displayed extensive phenotypic somaclonal variation - the cloned "offspring" were not genetically identical. They attributed most of this genetic variation to an increased base substitution frequency in the regenerant offspring but there may also be unknown epigentic factors as well.

Jiang et al. summarise:

...

... somatic mutation rates are characteristically higher than germline rates in multicellular organisms [26] and has important particular potential consequences for the evolution of plants, given that they frequently adopt life cycle strategies that involve regeneration from somatic tissues.

So, perhaps some of the variation we see in plant species which commonly propagate asexually actually arose during this process and not via sexual reproduction ... ? This would be good news for houseplants which are nearly always propagated asexually.

However, I am not sure whether this extends to potatoes.

Jiang et al. 2011, Current Biology, 21, 1385, Regenerant Arabidopsis Lineages Display a Distinct Genome-Wide Spectrum of Mutations Conferring Variant Phenotypes

pigmentation - How do animals perform detailed active camouflage?

We often see videos of octopuses and chameleons changing their color to suit their surroundings. If it was a simple color change from white to red, it'd be understandable, but some of these animals can change colors while incorporating a lot of detail.

How do they process so much information and mimic it. Is this a subconscious action, or do they actually draw a picture in their head and then 'print' it on their bodies? Does this ability come from birth or does it get better over time?

biochemistry - How do cells slowly degrade 5,5'-dibromo-4,4'-dichloro-indigo?

5,5'-dibromo-4,4'-dichloro-indigo is the product of X-gal cleavage, often used as a reporter with B-galactosidase. I've made the (unreferenced) observation that it seems as though the blue product slowly degrades over periods of time within the cell, allowing for cells to lose their blue coloration.

What mechanisms can explain the degradation of 5,5'-dibromo-4,4'-dichloro-indigo within cells?

genomes - Examples of intracellular parasites of medical or economic importance?

As Armatus pointed out above, all viruses are obligately intracellular, and their medical and economic importance cannot be overstated.

Many bacterial species live intracellularly. The arthropod specific Wolbachia has a wide variety of consequences for its host, including alteration of reproduction and sex ratios, induction of reproductive isolation possibly driving speciation, and conferring protection from some viral infections.

Eukaryotes can be intracellular parasites as well: Malaria is a well-known example. Toxoplasma gondii is another intracellular parasite that uses cats as a primary host, but can use other warm-blooded animals (such as humans, rats, and birds) as intermediate hosts. T. gondii infection has been shown to induce behavioral changes in rats, causing an attraction to cats (thereby increasing the chance that the parasite will infect the cat and sexually reproduce). There is also some evidence that T. gondii infection in humans causes behavioral and psychological changes such as decreased reaction times, and links to depression and suicide.

genetics - Possible Genotypes of 4 Alleles of Adh

Those Hardy-Weinberg equations are the general case, used for only two alleles. This question is basically answered here, for three alleles; you've got a situation of four alleles. That means you need to have:

$(p+q+r+s)^2=1$

Where $p$, $q$, $r$, and $s$ are the frequencies of your respective alleles. This expands out to the rather unwieldy:

$p^2+2pq+2pr+2ps+q^2+2qr+2qs+r^2+2rs+s^2=1$

Now it becomes a plug 'n chug assignment; simply assign the frequencies and calculate.

Assuming $p$ is Adh-1, $q$ is Adh-2, etc., $p^2=0.0121$, $2pq=0.1848$, and so on.

dna - Are all body atoms really recycled several times during a life?

Rudolf Shoenheimer and David Rittenberg were key figures in introducing the isotopic tracer technique to biology.

This technique, which may be dated to the discovery of deuterium by Urey in 1933, produced a revolution in biological thought.

Much of the early work was done at the Department of Biological Chemistry at Columbia University under the chairmanship of H. T. Clark.

Up to this time it was thought that the components of tissues were relatively stable, and that ingested food was metabolized immediately to provide a source of energy.

The first experiments showed that when deuterated fatty acids were fed to mice, most of the label was initially deposited in adipose tissue.

It was concluded that adipose tissue acts a 'fuel depot' that is in a state of metabolic flux and is the direct source of fatty acids burned as a fuel (see here for refs). Fats present in food are not primarily used an an immediate energy source.

When a stable isotope of nitrogen became available (N¹⁵), it was found that proteins were also 'in a state of dynamic flux' and were being continuously regenerated and broken down.

The first experiments were done with N¹⁵-labeled tyrosine and it it worth quoting from the paper (Studies in Protein Metabolism. VII The metabolism of tyrosine by D Rittenberg Rudolf Schoenheimer & S. Ratner)

The results indicate that in our rat the nitrogen of at least one
amino acid, tyrosine, was only partly excreted in the urine, while
almost half of it was retained in the body proteins.

Of this deposited nitrogen only a fraction was found attached to the original
carbon chain, namely to tyrosine, while the bulk was distributed over other
nitrogenous groups of the proteins

Shortly after giving a series of lectures at Harvard University in 1941, Shoenheimer took his own life. The lectures were published posthumously as a classic book called The Dynamic State of Body Constituents.

Further information about the early work on isotopes, their role in changing completely the way we think about metabolism, and the role of Columbia University in shepherding in this great era, may be found in the following open-access article by Eugene. P. Kennedy:

Hitler’s Gift and the Era of Biosynthesis

Another good reference on the work of Schoenheimer may be found here

---

So are all proteins broken down and regenerated? I know of any one exception and that is the lens crystallins where there is virtually no turnover
throughout the life of an individual.

The crystallins in our lens are synthesized at birth and remain with us virtually unchanged for life.

There is a very nice open-access paper on this published in PLOS One:

Radiocarbon Dating of the Human Eye Lens Crystallines Reveal Proteins without Carbon Turnover throughout Life

(Lynnerup et al. 2007)

human biology - What happens when we know that there is something that we forgot but we can't remember what it was?

It is a phenomenon known as room amnesia, some research has shown that your brain may use physical barriers like the room and doorways as a way to compartmentalize thoughts.
One article summarizes it here:

The researchers say that when you pass through a doorway, your mind
compartmentalizes your actions into separate episodes. Having moved
into a new episode, the brain archives the previous one, making it
less available for access. It’s as if you slam a mental door between
what you knew and…what was I saying?

This is the research.