Types of Dominance Punnett Squares Cont. Pp 183-184, 244

Complete Dominance One allele is completely dominant over the other the heterozygous phenotype is dominant in appearance

Incomplete Dominance Dominant allele is unable to completely mask the recessive allele the heterozygous phenotype is an intermediate (or blend) of the two alleles 3 phenotypes and 3 genotypes

Codominance Both alleles are expressed An individual that is heterozygous shows both traits at once 3 phenotypes and 3 genotypes N S NN NS N S NS SS

Sickle Cell Anemia

Codominance Sickle cell anemia N= normal RBC S = sickle RBC NN- normal NS – has both types of cells in blood SS- has only sickle cells N S NN NS N S NS SS