Codominance vs Pleiotropism
Location: Outside U.S.
Country: United States
Date: Spring 2010
What is the difference between codominance and pleiotropism?
Co-dominance is when you have two alleles that both are equally
visible in the phenotype. The classic example is blood types-there
are A type antigens and B type antigens that each alleles of the same
gene. If you get A from Mom and B from Dad you have red blood cells
with both types of antigens on them. Type O really means that that
allele doesn't code for an antigen, so both A and B are dominant over
Pleiotropy is when a gene can be expressed as many different
phenotypes throughout the body. Marfan syndrome is an example of a
disease that exhibits pleiotropy. It is a disorder that affect
collagen production, I believe, which can cause elongated limbs, a
weak aorta, difficulties in the lens of the eye, etc. These appear to
be unrelated but all owe their cause to a single gene. Here is a link
to other phenotypes that are pleiotropic.
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Update: June 2012