> In simple discussions of genetics one hears of dominant and recessive
> genes. Dominant genes are expressed, while recessive ones are not.
>> What is it exactly that makes one of a complementary pair of genes
> dominant and the other recessive? Also, is the domination complete
> (i.e. dominant gene expressed 100%, recessive gene expressed 0%) or
> is it more of a 90%/10% or 80%/20% situation?
>> I know that the laws of thermodynamics must be obeyed, so if you
> can explain this phenomenon using thermodynamic arguments I would
> appreciate it.
>> Greg King
This is rarely a question of thermodynamics but rather of kinetics.
A mutation that makes an enzyme from an allele less active
kinetically will be recessive to the `wild-type' enzyme. However, if
the enzyme activity has some critical threshold then if you only get
one wild-type activity and one slacker enzyme then you may be at the
border line of the requisite enzyme activity. This means that
environmental consideration which may modify enzyme activities and
demands become critical. That explains why two organisms of
approximately equivalent genotypes and heterozygous for the same two
alleles can have different phenotypes. Also the background genotype
can affect the critical activity need level. Both of these would
explain `penetrance' of a particular gene. Rarely do we deal with
whether a gene is `expressed' or not. In actuality, unless the
mutation is in the promoter/transcriptional control region, all
alleles are `expressed' as in making an RNA/mRNA. It is just that we
may only see a finished-functional product/protein from some alleles.
One could envision mutations that destabilize the protein product
made and therefore the product is rapidly degraded.
||Doug Rhoads || Dept. of Biological Sciences||
||drhoads at mercury.uark.edu || 601 Science Engineering ||
||drhoads at uafsysb.uark.edu || University of Arkansas ||
||501-575-3251 || Fayetteville, AR 72701 ||
|| My Dogma Just Got Run Over by Someone's Karma ||