Does heterogeneity in opsin genes demand selection pressure

Bob Friedman friedmar at biol.sc.edu
Fri May 4 11:13:25 EST 2001


"C.J.L. Wolf" <C.J.L.Wolf at ncl.ac.uk> wrote in message
> My question is whether, as is often stated, we must invoke positive
> selection pressure for the female monkeys that have enhanced colour vision
> in order to account for the maintainance of several opsin isoforms in the
> population. If the hardy-weinberg equilibrium applies to genes on the
> X-chromosome, presumably the proportion of individuals in the population
> that carry each alternative opsin gene should not change from generation
> to generation so there's no need to search for a reason for the
> continuation of established heterogeneity in the population. But I'm sure
> I remember vaguely some maths in a pop-science book that said that a
> million years from now we'd all end up with the same surname, as the
> statistics of surname inheritance tend to select names out at random. As
> an embryo is more likely to carry an X chromosome from its mother than its
> father, presumably similar stats should apply?

The effects of genetic drift are also important.  See:
http://www.evotutor.org/GenDrift/GD2A.html
The example you made about surnames -- does it also model mutations?
Did you try a journal search of population genetics studies of the above?
If there are no studies then you can't presume whether the gene frequencies
are in H-W equil.

> If no selection pressure is necessary to explain the maintainance of the
> alternative alleles in the population, would it still be a prerequisite
> for their establishment in a reasonable proportion of individuals? In
> fact, only 3 alternative forms of the pigment are present in Marmosets.

Possibly; you could model different strengths of selection versus the
initial frequency in the population.
http://www.evotutor.org/EvoGen/EG1A.html

> Kit Wolf



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