The Long Terms Effects of Evolution...Take a Chance -Reply

Clinton Hale c.hale at gen.latrobe.edu.au
Thu Dec 18 00:41:55 EST 1997

Hardy -Weinberg equilibrium occurs under the following parameters:
large population size;
no mutation;
no migration;
no selection;
random mating.

The Hardy-Weinberg proportion for sex-linked traits are p (normal
phenotype) and q (affected phenotype) for the males and p^2 (normal
phenotype), 2pq (normal carrier phenotype) and q^2 (affected phenotype)
for the females (assuming one gene with two alleles) (^2 = squared).

The only way there can be a "slight shift" in the HW proportions is if
the allele frequencies alter.  By removing the q males and the q^2
females the shift is unkown until we know what the allele frequencies
are, but then we are no longer in Hardy-Weinberg equilibrium because
there is extreme selection against these two genotypes (see above).

The frequency of q males is 1/5,000 births for Haemophilia A and 1/30,000
for Haemophilia B in the U.K. (Connor,J.M. and Ferguson-Smith,M.A.  1984,
Essential Medical Genetics, Blackwell Scientific Publications).

Steven Projan wrote:

> Jabriol wrote:
> > so if we get rid..uh.. isolate every hemophiliac in the world, and
> > casra...uh
> > nuterize them.. would we remove the defective gene
> No:  as is the case with most all recessive traits there may be a
> slight shift in what is called the "Hardy-Weinberg equilibrium"
> (which is reallly for autosomal recessive, not sex linked, traits)
> but only to the extent that hemophiliacs now have children (which
> accounts for a small percentage of the transmission of the gene).
> This is true even though the defective gene (coding for clotting
> factor 8) for most hemophiliacs is found on the X chromosome making
> this a "sex linked" characteristic (meaning that male offspring of a
> heterozygous mother have a 50% of being hemophiliacs).
> Remember Queen Victoria?  The Tsaravich? Rasputin?  Don't we teach
> this stuff in high school anymore?
> The only way to remove such a gene from the population is for both
> hemophiliacs and carriers of the trait to refrain from procreating.
> While this may sound like a good idea where do we draw the line on
> this kind of practice for inherited traits?  Homosexuality? Baldness?
> Votes for Republicans?
> Het, I'm a bacteriologist, what do I know?
> Steve Projan
> Wyeth-Ayerst Labs

Clinton Hale,
School of Genetics and Human Variation,
La Trobe University,
Bundoora, Victoria, 3083,

Phone +61 (0)3 9479 2256
Fax +61 (0)3 9479 2480

Email c.hale at gen.latrobe.edu.au
URL http://www.gen.latrobe.edu.au/microscopy

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