1.  Simple Dominance  The heterozygous expresses the dominant phenotype 1 gene 2 alleles 2 phenotypes  Incomplete Dominance  The heterozygous expresses less than the homozygous dominant individual so it seems incomplete 1 gene 2 alleles 3 phenotypes  Codominance  The heterozygous expresses both dominant alleles 1 gene 2 dominant alleles 3 phenotypes

2.  Multiple alleles  3 or more alleles interact to give different phenotypes of the same gene 1 gene 3 or more alleles Multiple phenotypes  Blood typing  Polygeneic  2 or more genes interact to give a wide range of different phenotypes 2 or more genes 2 alleles Multiple variations of phenotypes  Hair and eye color  Epistasis  A gene controls the expression of a different gene  Rooster combs  Black, Chocolate, Yellow labs

3.  Presence or absence of AB antigens  Type A – A antigen I A I A or I A i  Type B – B antigen I B I B or I B i  Type AB – Both A and B antigen IAIBIAIB  Type O – none of the antigens ii  Because antigens are recognized by the immune system the right blood must be used for transfusions Wrong blood = the immune system will attack it AB = receive any bloodAB = donate to AB only O = receive only OO = donate to anyone  RH factors Simple dominance (not the whole story but for our sake) Have Rh antigen = + (dominant) Don’t have Rh antigen = – (recessive) Immune system during pregnancy