Coat color evolution--is there evidence for new mutations?

[Mercer (John Mercer)]

@T_aquaticus

With that being said, let’s discuss what I did consider. I will mainly be working from this PNAS paper:

I am too; that should have been obvious, as I already pointed out above that you misrepresented the data shown in Fig. 1A.

The only work you are doing here is goalpost moving.

Here’s your claim from which you are trying to divert attention:

@T_aquaticus

A new mutation resulting in black fur allowed the mice to take up a new niche in environments dominated by black basalt rocks.

New mutation. Let’s keep our eye on that ball.

This is very relevant to my point that current educational practices fail miserably to teach people that the reservoir of existing variation is ~1000000-fold larger than the number of new mutations per generation.

You seem to be a poster boy for this failure, as you immediately claimed that the mutation was new and allowed the mice to take up a new niche.

My point is that there is no evidence for your claim that the mutation was new.

You still haven’t presented any.

@T_aquaticus

First, is the black coat color allele dominant in the genetic background of the wild population? The evidence in the paper seems to back this up:

It obviously was for the only population they studied in detail. I’m disputing your more general claim that black alleles are dominant. They aren’t.

@T_aquaticus

Every black mouse at the Pinicate locale had 4 specific polymorphisms. Every one of them.

What does that have to do with your claim that the mutation occurred after the selection was present?

@T_aquaticus

On top of that, the coloration was discrete:

I’m quite familiar with the locus, thanks. What does that have to do with your claim that the mutation occurred after the selection was present? Are the progeny of a C57BL/6 x C3H cross discretely colored?

@T_aquaticus

To summarize these points, the black allele was dominant in this wild population which is a very common feature for dark coloration alleles in mice and other organisms.

I’d like to see some support for that claim for mice.

@T_aquaticus

Is it possible that there is some very rare allele in the wild population that they missed?

Straw man. I’m not claiming that they missed anything. I’m claiming that you don’t know when the mutation occurred. There’s no reason for the adjective “new.”

This is about selection acting on the huge reservoir of existing variation, remember?

@T_aquaticus

If there is such an allele then it is either rare or geographically limited, both of which can’t explain the distribution of coat color.

You seem to be either very confused or are deliberately obfuscating. I’m challenging your claim that the mutation was a new one.

@T_aquaticus

In lighter colored desert in the immediate vicinity to the basalt flows, they trapped 11 mice and only 1 had dark fur.

Yes. As I noted, that falsifies your misrepresentation of the data:

@T_aquaticus

As you move away from the lava flows you don’t find the dominant black allele…

But they did. Why did you do misrepresent the data?

@T_aquaticus

If this dominant black allele is not seeing strong negative selection in the light colored desert regions then we would expect to see about 75% of mice with dark fur.

So what? I’m disputing your claim that the mutation is new. How does that relate to your claim?

@T_aquaticus

The authors also reported that there was sufficient admixture between the populations so that we should see the black allele in the light colored desert regions if there was a lack of negative selection against the allele:

There’s obviously strong selection. How does that even suggest, much less demonstrate, that the mutation is new?

@T_aquaticus

I remember the age of the lava flows being recent, which further supports the emergence of the black allele in the brown population.

That has nothing to do with whether the allele was already present in the ancestral population. Of course the allele has become fixed. When did a mutation produce that allele, Taq? There’s no evidence that it happened after the mice encountered the basalt flows.

@T_aquaticus

However, there is more info in the paper that supports the conclusion that the black allele is a recent addition to the population:

It says “the recent action of positive selection.” It doesn’t say “a new mutation.”

@T_aquaticus

To me, and to the authors of the paper, this suggests independent genetic adaptations to the black basalt environments that emerged in the brown coat colored population.

I agree that the frequency of the black allele has been increased by selection, but that wasn’t your claim. Your claim was that it was a new mutation:

@T_aquaticus

A new mutation resulting in black fur allowed the mice to take up a new niche in environments dominated by black basalt rocks.

Why are you pretending that you claimed something very different?

Anyway, you are certainly demonstrating that even scientists don’t see the ratio of existing to new variation clearly.

@T_aquaticus

For the most part, I am echoing the conclusions drawn by the authors in the PNAS paper. You can call them my assertions, but they are the conclusions found in the paper.

Where will I find your assertion that the mutation is new in the paper? I don’t see any problems with the paper; only with your claim that the mutation is new.

This is why we need to teach students that Darwin only observed existing variation. This is why teaching about mutation first makes students susceptible to pseudoscientific propaganda.