Testing Founder Effect Hypothesis in Humans and Neanderthals

[Monique]

I thought it would be nice for you guys to play around with this, I have got my answer, let's see if anyone views it the same way.

There is a gene coding for a protein. The protein can either have amino acid A on the end or the aminoacid B. It turns out that humans only have amino acid B, since we have a deletion in the gene.

Chimpansees have amino acid A though, so the deletion took place after we diverged from the chimp. Now, scientists isolated proteins from Neanderthaler bone and found that also here, only form B is present.

So the deletion predates our common ancestor, about 2.7 Mya (million year ago).

Is it thinkable that a founder effect has caused humans to loose from A of the gene, and how would you test that hypothesis?

 

[Monique]

Let's shortly explain founder effect, it is a genetic term for the situation where the size of a population shrinks dramatically, reducing the genetic pool.

 

[selfAdjoint]

Do they have enough protein from different Neandertal individuals to be confident that _all_ Neandertals had only B? I am assuming here that Chimpanzees have both A & B (that is, each Chimp has either A or B).

So, the mutation happened to one individual in a population that otherwise had individuals with A or B. That mutated individual mated and on probability half of its children had the mutation (unless it was sex-linked, which you didn't say). Assume normal outbreeding and half of the children of that half will have the mutation and all of the chilren of the other half will lack it. So in the third generation the proportion of those who have to all descendents will be 1/4, and it goes as inverse powers of 2 assuming outbreeding at every stage. So if the subsequent homo species are descended from a random sample of the precursor population, the assumption of outbreeding makes it overwhelmingly likely that some unmutated individuals will be in the sample, and the B & A possibility will be passed on. Since it wasn't the assumption of unrestricted out breeding is false, which is equivalent to saying founder effect.

 

[Monique]

Yes, the chimp had A and B. But then how would you explain that the humans tested only have from B? It seems to be a disadvantage, since form A is still needed and is taken up with the diet (meat).

So there are two possibilities:
1) the deletion is an evolutionary advantage, but then why isn't there the same thing happening in the chimp.
2) the deletion arose in the population by a founder effect, how would you go about testing such hypothesis and would such a hypothesis be possible?

 

[FZ+]

What about the possibility that we have this all wrong?

That we are not talking about a case of deletion, but that the chimp/human common ancestor itself only had B? In this case, we have the chimp branch separately developing A after the divergence, whilst the human/neaderthal branch failed to do so.

Any evidence to disprove/prove this?