Dominant/Recessive Genes

Ken Brown rkjb at cix.compulink.co.uk
Mon Feb 28 16:37:02 EST 1994


> Recessive genes are generally not "good" for the organism, yes?

Well, no. The gene might be good, bad, or more likely indifferent.
There are many mechanisms that make a gene recessive & they are, AFAIK,
unrelated to whether it is "good" or not (what harm do my grey eyes do me?)

If what you mean is that deleterious mutations can sometimes survive in a
population if they happen to be recessive, then you've answered your own next
question....

> If so why do they exist? Why do two alleles exist together?

There isn't neccessarily any purpose to them at all, any more than there is
to any other gene. They just exist. Genes (recessive or dominant) that help
the organism they code for to reproduce will tend to be passed on to the next
generation. Those that hinder reproduction will not be.

AFAIK most mutations are neutral, they make no difference one way or the
other.  Most of the rest are fatal. A few are advantageous. So from normal
processes of mutation & reproduction we'd expect to see a vast variety of
geneomes. Most loci are polymorphic.

Once upon a time many biologists thought in terms of a "perfect" or "normal"
specimen of each species or race, an ideal genotype which was perfectly
fitted to it's environment & would remain stable for a long period of time.
This meant that the observed variation within species was a problem that had
to be explained away.

These days, as far as I know (like you I'm a programmer, not a professional
biologist) they tend to look on it the other way round. Variation is
expected, when little variation is found withing a species (like Cheetahs)
that is seen as a problem, something that needs to be explained.



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