Newsgroups: comp.ai.genetic
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From: timt@aisb.ed.ac.uk (Tim Taylor)
Subject: Re: Dominant/Recessive genes, How do they know?
Message-ID: <DJoMvn.KF5@aisb.ed.ac.uk>
Sender: timt@weed (Tim Taylor)
Organization: Dept AI, Edinburgh University, Scotland
References:  <4as5le$h5f@krone.daimi.aau.dk>
Date: Sat, 16 Dec 1995 13:59:46 GMT
Lines: 24

Morten,

Here's a brief picture of dominant/recessive alleles, as far as
I understand them. I'm sure there's much more that can be said,
but this at least gives an intuitive feel for what's going on...

Genes code the production of proteins which are used by the cell
either for catalysing chemical reactions (enzymes), or for various
other functions (e.g. structural). A recessive allele is generally
a version of a gene which _lacks_ the ability to produce a protein
that the dominant allele _does_ produce. Therefore, in a diploid
system, a heterozygous cell (one dominant allele, one recessive)
still produces _some_ of the protein (but less than a homozygous
dominant) - in many cases this is enough for the expression of the
dominant phenotype. It is only in a cell that is homozygous
recessive that _none_ of the protein gets produced, so only then
is the recessive phenotype expressed.

Tim.

--------------------------------------------------------------------------
Tim Taylor, Department of Artificial Intelligence, University of Edinburgh
             tel +44-(0)131-650-3084/3081/4493 fax -650-6899
             home page http://www.dai.ed.ac.uk/students/timt
