Re: Sequence Homology

R. Joel Duff (Virkotto@intrnet.net)
Mon, 15 Dec 1997 16:10:09 -0600 (CST)

>At 09:36 AM 12/15/97 -0600, Joel wrote:
>>Here is my short response, I'll try to put together a more explicit example
>>later. My first reaction is to point out the number of times that one can
>>reconstruct phylogentic relationships of a particular group with different
>>genes and get the same result. Etc.
>
>I would like to suggest that logically this line of reasoning is consistent
>equally with an evolutionary hypothesis and with creation by a God who was
>wise enough to realize (as sometimes we ourselves seem not to be) that the
>more similar two organisms are, the more similar their (whatever) need to
>be.

Art,
Yes, I think it is. I think this leaves us with the argument that God
created with the appearance of ancestry which opens a whole other set of
questions.
I don't see any a-priori reason for believing that similar organisms have
to have similar gene sequences if the function is the same for all. I have
more trouble with the observation that spacer sequences such as the ITS
between the nuclear ribosomal genes also shows such similarities. This
requires that God also intentionally made these sequences similar (though
not the same) between different species that morphologically similar. What
do we do also about convergent evolution wherein we see two organisms that
appear to be mophologically similar externally but are internally quite
different? If similar genes correspond to similar appearences then why
aren't these organims so similar in their DNA sequences for the same genes?

>The question I would like to see addressed is the following: (specifically
>to the issue raised by Lorne) The very complex (some are 24 pass proteins
>with gates and in the case of the sodium channel, a ball and chain to plug
>the channel temporarily while the gate is reestablished) ion channel
>proteins of insects and humans are essentially identical in structure
>(ignoring for the moment the differences in amino acid composition which
>fit the molecules for their specific environments) and in function to the
>point that most of what we knew about the system in humans we have learned
>from the study of the system in insects (up until the last few years when
>recombinant technology came in). Focusing attention on the minor
>differences that distinguish organisms from one another only serves to beg
>the question about the origin of the complexity itself. For this we are
>left with a giant question mark.
>
>If evolution is the correct explanation for origins, then the common
>ancestor of insects and man must have had these same ion channel proteins
>in essentially their current configuration. The same logic applies to
>virtually all of the molecular complexity recognized in modern organisms,
>including the developmental genes and the general scheme of development
>shared by insects and man.

These are good questions for which I don't have any easy answers but I am
not at all familiar with ion channels (it should be obvious by now my
knowledge of animal systems is quite limited). I will be interested in any
other responses that you get.

rjd

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