identical mutations

Dave Williams PROFDHW at AOL.COM
Mon May 5 07:26:02 CDT 1997

In a message dated 5/5/97 2:16:42 AM, Doug Yanega wrote:

>After all, the implication is that all the individuals in the
>population have a portion of their genome (obviously somewhat conserved
>since it has to be virtually identical across the population) which is only
>one or two simple nucleotide changes away from a functionally superior
>alternative, so the same new beneficial allele can crop up repeatedly. This
>seems like an unlikely set of circumstances to me, at least at first

Content snipped.

>But if population geneticists believe that beneficial mutations *often*
>have multiple origins, has this been taken into consideration by molecular
>systematists, and/or is it considered irrelevant? Or am I missing something
>and just asleep at the switch today?

Do recessive mutations need to be identical to be identically effective? If a
debilitating or liability laden dominant gene can be deactivated by rendering
the protein associated with its locus ineffective through mutation then ANY
such incapacitating mutation would be helpful, would it not? It seems likely
that there may be several to many possible amino acid sites at which a
substitution would change the tertiary structure of the protein. Thus
beneficial recessives might easily have multiple origins. Am I genetically
naive or missing something? How do we know, in the sense of classical
genetics, that all recessive alleles are identical?

The predominance of "type O" blood in many human populations is a testament
to the effectiveness of the recessive condition in enhancing fitness by
rendering the gene responsible for the (now, apparently) useless blood cell
surface agglutinogens ineffective in the production of those agglutinogens,
and the organism less open to infection by members of its
agglutinogen-mimicking body flora. Or so I thought.

Dave Williams
Science Division
Anne Arundel Community College
Arnold, MD 21012
Vmail: 410-541-2265
Email: profdhw at

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