Incomplete Dominance

The ______ phenotype is between those of the two _______

The heterozygous phenotype is between those of the two homozygotes 

Example: Familial hypercholesterolemia (FH)

Heterozygote has approx. 1/2 the normal # of receptors in liver for LDL cholesterol

Homozygous, for the mutant allele, lacks the receptor so their serum cholesterol level is very high

Codominance:Heterozygous phenotype results from expression of both alleles

Example: A.B.O. gene encodes cell surface glycoprotein

     Explain how this is possible (taken right from notes)

    I^A allele produces A antigen

I^B allele produces B antigen

i (I^O) allele does not produce an antigen

   Alleles I^A and I^B are codominant, and both are completely dominant to i (I^O)