* Incomplete Dominance
characterized by an intermediate phenotype in heterozygote

+ multiple alleles - multiple versions of a gene

+ codominance - both alleles are expressed in heterozygous individuals

+ in blood types; a & b are codominant; o is recessive

** ABO Blood Type
Blood type alleles: I^A I^B, i

Possible Genotypes:

| Type A  | I^A I^A | I^A i |
| Type B  | I^B I^B | I^B i |
| Type AB | I^A I^B | -    |
| Type O  | ii    | -    |

** 
ii