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Re: Digit loss
Philidor11 (firstname.lastname@example.org) wrote:
<You could also expect to see the digits disappear and reappear,
much as 6 toed cats have 5 toed offspring. Until variation
appears extensively in the record, isn't it most appropriate to
think that at some point in the past there was an advantage to a
certain number of digits and that the capability of
re-expressing lost digits had disappeared?>
Something that has been overlooked in this thread is that even
if an element is lost in the genome, so that there is not longer
a way to code for a fifth digit, say, there is still a way to
have a fifth digit, and we see this kind of genetic loophole in
giraffes and Phillidor's cat example: duplication. An element
can easily be duplicated by transcription in the genetic code.
Giraffes have doubled, exactly, a central cervical, and the
sixth finger of the cat is a duplicate of the first, so that
there are technically two left polleces, etc. I had a cat with
this, and so I remember distinctly how identical these two
digits were. This can also explain sauropod neck development,
and as Wilson and Sereno, 1998, there are conscription factors
in the cervicalization of dorsals, but in euhelopodids [possibly
paraphyletic] and the diplodocid lineages, there are more
cervicals than can be explained by transforming one set into
another. Here duplication is the answer.
Jaime A. Headden
Where the Wind Comes Sweeping Down the Pampas!!!!
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