In article <1onudrINNmi7 at shelley.u.washington.edu>
toby at stein.u.washington.edu (Toby Bradshaw) writes:
> In article <1onpe4INNi7r at shelley.u.washington.edu>
>bishopj at botany.washington.edu writes:
>> [snip]
>> >Furthermore, among mutations arising in a population
>>recessivity is clearly the
> >rule.
>> I doubt this is true. For visible mutations, maybe. If
>it were
> _generally_ true, narrow sense heritability estimates for
>quantitative
> traits would always be low, and that's not the case.
>Yes, I would definitely like to recant that statement.
Neutrality is the rule. Most mutations which do have an
effect on enzyme activity are expected to decrease it.
Because of the buffering effect of enzyme networks, these
mutations may have little or no phenotypic effect, i.e.
they have no detectable effect on flux through the enzyme
system. When mutations occur which do increase catalytic
activity, they are expected to be undetectable, since they
will already be on the plateau of the flux-enzyme activity
curve. This class of undetectable mutations would
contribute to the genetic variance in a quantitative trait.
When a mutation does have a detectable effect, it will
usually be associated with a large decrease in enzyme
activity, and will be recessive or partially so.
--
John Bishop
Department of Botany
University of Washington, Seattle
bishopj at botany.washington.edu
