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Unformatted text preview: Codominance and Multiple Alleles- Example: ABO blood group Up to this point, we have discussed two possible alleles for any gene locus. For example, at the flower color locus, there is either the red or the white allele (A or a). With human blood types, there are three alleles: A, B, or O. This is referred to as multiple alleles . I is dominant to i. There are two forms of I: I A and I B but only one form of i. 6 possible genotypes, 4 phenotypes: I A I A and I A i = blood type A I B I B and I B i = blood type B I A I B = blood type AB i i = blood type O People with blood type A have a specific kind of carbohydrate chain on the surface of their red blood cell. The carbohydrate chain is attached to a membrane protein or lipid. Blood type B cells have have a different carbohydrate chain. Type AB cells have both A and B chains. I A and I B are codominant because both phenotypes are expressed; there is no blending Codominance is different than Incomplete dominance (blending)....
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- Fall '10