Re: [asa] Shark mutation

From: D. F. Siemens, Jr. <>
Date: Thu Aug 23 2007 - 16:31:49 EDT

On Thu, 23 Aug 2007 14:07:36 -0400 "Alexanian, Moorad"
<> writes:
> Does the "closeness" of two species imply an ancestral connection
> between them? Could the extra #21 dyad that gives rise to Down
> syndrome have come about by a mutation? Do normal humans then
> evolved from Down syndrome ancestors?
> Moorad
The syndrome is trisomy 21, that is, an extra copy of the chromosome.
This is an accident during cell duplication. There is no mutation
involved normally. However, occasionally a piece of the chromosome is
attached to a different chromosome, normally through crossover. But this
is not a point mutation, like the pair noted in the malaria parasite.

By the way, there seem to be three species of plasmodia causing human
malaria, plus I know not how many species infecting mice and birds and
perhaps other creatures. It strikes me that it would be of interest to
determine the variations which allow infections and various creatures.

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Received on Thu Aug 23 16:34:02 2007

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