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Name: Rahul
Status: Other
Grade:  12+
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 O.

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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