Max Cates (cates at biochem.purdue.edu) wrote:
: With VERY few exceptions, this is the way one-allele dominance/recessive
: cases work. Incomplete dominance (like in Mendel's pea flowers:
: red (RR) + white (WW) =pink(RW)) arises when one copy of the gene
: producing functional protein isn't quite enough to make all the necessary
: protein, or when the inactive protein can competitively inhibit the
: active one.
:...or if both alleles make valid enzymes. The A and B blood antigens
fall into this category (and O blood-type is a defective allele of
the ABO locus which cannot make a functional protein). AB individuals
make both the A antigen and the B antigen.
BTW, someone once wrote a very nice summary of the various ways
a dominant/recessive system can be explained at the molecular level.
(there are a number of special cases)
It should be in the bionet archives:
Department of Cellular and Developmental Biology
Department of Genetics / HHMI
robison at mito.harvard.edu