Re: Good Mutations.

R. Joel Duff (Virkotto@intrnet.net)
Wed, 3 Dec 1997 16:56:38 -0600 (CST)

>At 03:52 PM 12/2/97 -0600, R. Joel Duff wrote:
>Moorad wrote:
>
>>>I am not sure I understand. Is it possible that the bacteria have a sort of
>>>bell-shaped curve of characteristics that determine what the bacteria is and
>>>by means of environmental changes we can select the parts of the bell-curve
>>>which we desire. Sort as animal breeding. Do we indeed have to talk of
>>>mutations? Can we tell at the molecular level? What makes us say that we are
>>>dealing then with the same bacteria?
>>
>>Moorad,
>>
>>I think there is much less room for phenotypic variation in this case.
>>Usually in such an experiment one plates bacteria onto a media and picks
>>bacteria from a single colony. It seems safe to assume that all the
>>bacteria in that colony came from a single bacteria. One then grows
>>bacteria from that single colony up in some liquid media and then plates
>>out several billion bacteria onto a different media (in this case higher
>>salt concentration). Only a few of the millions/billions of bacteria may
>>manage to survive. Since these bacteria all came from a single bacteria at
>>one point we are definitely dealing with the "same bacteria." Rather than
>>selection on a bell shape curve of characteristics due to inherent
>>variation, it is more likely that the ability to survive on the salt media
>>is due to a point mutation of some type that enables the bacteria to
>>acquire an enhanced ability to deal with a high salt environment. Hope
>>that helps.
>>
>>Joel
>
>In summary, from a particular kind of dog, say a chihuahua, we cannot ever
>get a Saint Bernard. Is that your argument?

Moorad,

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.

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.

Joel

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