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dominant genes

Daniel Weinreich dmw at MCZ.HARVARD.EDU
Fri Jan 6 14:21:58 EST 1995

On 6 Jan 1995, S. LAURA ADAMKEWICZ wrote:

> On 4 Jan 1995, Henry T Robertson wrote:
> > Hello, is there a reason why some traits are dominant rather than recessive?
> > Are dominant genes better suited for the environment?  If so, is there
> > a logical reason why they became dominant genes?
> > 
> > Your e-mail replies appreciated.  
> > 
> Sir Ronald Fisher analyzed this problem thoroughly back in the early days 
> of population genetics.  You should read his discussion of the evolution 
> of dominance in "The Genetical Theory of Natural Selection"...

I may have muddled this up since hearing one or more lectures on the
topic, but my impression is that Fisher's evolution of dominance arguments
are not the only ones worth considering.  Alternatives focus on
physiological reasons for dominance, rather than selection for dominance.

Sewall Wright postulated that the shape of the curve which described an
average enzyme's throughput as a function of enzyme concentration very
quickly approachs an asymptote.  Thus a single dose of a gene
(heterozygote) may give very nearly identical phenotype as a double dose. 
See Am Nat 63:24.

The "modern" view is due to Kacsher and Burns, in which a single enzyme is
viewed as one "cog" in a complex pathway; phenotype is a character of the
whole pathway and not just dosage of a single enzyme.  This analysis gives
curves similar to those Wright imagined.  See Genetics 97:639.

Daniel M. Weinreich			email: dmw at mcz.harvard.edu
Harvard University 			usmail: 26 Oxford Street
Museum of Comparative Zoology			Cambridge, MA 02138
voice: (617) 495-1954			fax: (617) 495-5667

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