Re: Good Mutations.

Moorad Alexanian (alexanian@UNCWIL.EDU)
Fri, 05 Dec 1997 17:15:16 -0500 (EST)

At 04:56 PM 12/3/97 -0600, R. Joel Duff wrote:

>>In summary, from a particular kind of dog, say a chihuahua, we cannot ever
>>get a Saint Bernard. Is that your argument?
>I don't think so. I'm not sure that the question of dog breeds contains
>gist of the same argument but I'll comment on it anyway. Not knowing much
>about the history of dog breeds or having any genetic studies indicating
>the amount of genetic variability residing in chihuahuas or Saint Bernards
>I would go out on a limb and say that we could not expect to get a Saint
>Bernard out of a Chihuahua. Remember that both dogs (and other dog breeds
>for that matter) were derived from breeding of wild dogs. Also not all dog
>breed necessarily came from the domestication of just a small number of
>wild dogs from a single population but were likely domesticated from many
>differnt wild dogs from different populations. The net effect of this is
>that there was a large pool of natural variation to draw upon in breeding
>programs. Thus it was not new mutations that are being drawn upon to
>produce new breeds but mixing of a large gene pool.
>This is completely different than taking a single dog breed like a
>Chihuahua and selecting features overtime and ending up with a Saint
>Bernard. The Chihuahua contains only a small subset of the total genetic
>variability in the gene pool of all dogs and so by themselves have
>effectively lost a large number of genes that would be needed to make a
>Saint Bernard. Only by going back to the "stock" could one "recreate" a
>Saint Bernard. I don't know that much about dog genetics so I might be
>wrong. The example I usually use is that of corn varieties. You would be
>hard pressed to make popcorn out of sweet corn because each of the five
>varieties of corn has been so selectively inbred that there is virtually no
>genetic variation and thus very little oportunity for deriving one variety
>from another. Only through hybridization can one reclaim genes that have
>been lost in a particular lineage.

Can these questions be settled at the molecular level? That is, wouldn't the
complete knowledge of the chihuahua genome and that of the Saint Bernard
answer our question?

>One question that comes of this that I have always had for global flood
>advocates that never seems to be addressed specifically is where the
>genetic variation came from that allowed the diversification of animals
>after the flood. In the dog breed example. Two dogs can only contain so
>much genetic diversity and yet we see they being held up as the example of
>microevolution. What the YECs often fail to point out is that dog breeds
>were derived from selection on traits from an already large genetic pool
>(large population of wild dog species/subspecies). Were did that genetic
>pool come from in the first place?? For example focussing on a single gene
>(for this example I don't have specific data) I would expect there may be
>30 or 40 varieties among dog breeds collectively. At best there would only
>have been a couple of varieties of that gene in the two dogs that jumped
>off the ark. One must postulate incredible rates of necleotide
>substitutions in order to accomodate the amount of variation in just
>domestic dog breed not to mention wild dogs and their possible relatives.


These are interesting questions which ought to be answerable the day we know
what every species is at the molecular level. I do not claim to know.