In article <BRIANF.93Mar24160949 at dna.uvm.edu> brianf at dna.uvm.edu (Brain Foley) writes:
>I was mislead earlier, in part because I was not familiar with the way
>in which you use the terms "dominance" and "recessive". In my
>training, "dominant" means only that one copy of the gene will produce
>the phenotype being looked at (i.e. yellow/green heterozygote pea pods
>will be green; green is dominant over yellow), it says nothing about
>whether the dominant or recessive allele provides better "fitness".
>>It is in this regard that I feel that new knowledge has changed the
>way we should look at genetics. Using green and yellow pods as an
>example, we might now find out that yellow peas lack the gene for
>green pigments, or we might find out that they produce a yellow
>pigment. Using visual analysis, green is the dominant gene, but using
>an assay that detects only yellow pigments, yellow is the dominant
>gene. This is where I have a problem: dominance or recesiveness in
>these cases is in the eye of the beholder.
Not so. It is as you described in your opening paragraph; the
phenotype of the heterozygote determines dominance. In the
example immediately above, yellow is not dominant to green no
matter how you look at it. In the yellow/green heterozygote there
is yellow pigment, and in the yellow/yellow homozygote there is
yellow pigment. So far, so good. The difficulty is that there
is yellow pigment in the green/green homozygote, too
>Many students in molecular genetics are confused about what "dominant"
>and "recesive" mean. Most often, recessive means that some gene
>product is lacking, so if a cell-cell hybrid is made, the cell with
>the dominant phenotype provides the lacking enzyme. But this is not
>always the case.
OK. It's late and my memory isn't the best. I'm having a hard
time coming up with an exception to the above. Care to help me
out?
>I guess I was sticking my neck out to post to molbio.evolution when I
>am not a student of population biology, but I think that is important
>for all biologists to use the same definitions for the same terms. I
>think that "dominant" can be a fuzzy term in some cases now.
You'll have to provide an example to convince me that dominance
is a fuzzy term. I think you understand the definition, but you
think it doesn't apply all the time. Your example above is not
an example of the failure of the definition, IMHO.
>********************************************************************
>* Brian Foley * If we knew what we were doing *
>* Molecular Genetics Dept. * it wouldn't be called research *
>* University of Vermont * *
>********************************************************************
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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Around here, we like to think we know what we're doing, even though
we might not know what the answer will be :)
Toby Bradshaw |
Department of Biochemistry | Will make genetic linkage maps
and College of Forest Resources | for food.
University of Washington, Seattle |
toby at u.washington.edu |
