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

2. Incomplete Dominance:
Hybrids show a BLENDING of both alleles.

3. Co-Dominance:
Both alleles are fully expressed.

4. 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 *

5. 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

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

7. 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?

8. 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?

9. 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?

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