Re: Hardy-Weinberg lawt

From: EKurtz (NoJunk_at_ForgetIt.com)
Date: 06/29/04 

Date: Tue, 29 Jun 2004 16:10:46 +0000 (UTC)

"John Edser" <edser@tpg.com.au> wrote
> Please confirm of deny that the HW "distribution"
> represents a defined population genetics zero state,
> i.e. a defined state where no significant change
> exists.

It is a state of equilibrium with respect to the populational proportions
of genotypes for a given locus, based on certain simplifying assumptions,
among them - no selection. That's why it is called Hardy-Weinberg
*Equilibrium*. If a population is currently *not* in HWE, but satisfies the
assumptions, it will rapidly reach HWE (ie in a few generations, or one
generation if all members breed at the same time).
If a real population does not satisfy HWE for a given locus, eg if the
genotype represented by the homozygous rare allele is lower in frequency
than would be expected under HWE, it is likely that that locus has been
subject to selection, either against the rare allele or in favor of the
common allele. Thus, departure from HWE is a sign that a locus may have been
subject to selection, which is why HWE is important.

> JE:-
> Is it true to suggest that HW "law"
> only represents a zero state because
> HW represents the maximal state of
> reproduction that exists within Pascale's
> Triangle?

This is meaningless, as far as I can tell; what is the "maximal state of
reproduction"? How can a state of reproduction exist in Pascal's or anybody
else's triangle? In any case, in the case of 3 or more alleles, Pascal's
triangle (note spelling) coefficients no longer apply. Better to forget
Pascal and concentrate on the assumptions that lie behind HWE, and the
manner in which the genotype proportions are derived.