There are some cases in nature where one allele is not dominant over another.

Incomplete Dominance: Hybrids show a BLENDING of both alleles.

Co-Dominance: Both alleles are fully expressed.

Multiple Alleles For each trait studied by Mendel, there were only 2 possible alleles per gene. However, it is possible to have more than 2 alleles per gene. Many genes have multiple alleles. For 2 alleles, the dominant allele is expressed over the recessive. For multiple alleles, a dominance hierarchy exists, determining which allele will be expressed. * But remember, an individual can only have 2 alleles for a specific trait *

Example Blood types in humans have 4 phenotypes: A, B, AB, O The gene for blood type has 3 alleles: IA, IB, I So, 3 alleles control blood type, but an individual can only have 2 alleles for a specific trait. This results in 6 different genotypes. ___ ___ ___ ___ ___ ___ IA and IB direct the synthesis of proteins A and B which are found on the surface of RBCs. I does not direct the synthesis of any proteins

Phenotype Genotype(s) i is recessive to IA and IB IA and IB are co-dominant Phenotype Genotype(s) A B AB O

A male has blood type AB and a female is heterozygous for blood type B A male has blood type AB and a female is heterozygous for blood type B. What is the genotypic and phenotypic ratios of the F1 generation?

2. A male is homozygous for blood type B and a female is heterozygous for blood type A. What is the genotypic and phenotypic ratios of the F1 generation?

3. A male has blood type O and a female has blood type AB 3. A male has blood type O and a female has blood type AB. What is the genotypic and phenotypic ratios of the F1 generation?

Practice Problems Worksheet Read and make notes p. 142-145 p. 144 #1-3; p. 145 #2,5-12