1. Incomplete Dominance and Codominance

2. In Mendel’s work, alleles were either dominant or recessive. If yellow (Y) is dominant to green (y), then: –YY will be yellow –Yy will be yellow –yy will be green Notice that we only got 2 different phenotypes However, sometimes we get 3 different phenotypes…

3. Incomplete Dominance In the case of incomplete dominance, two alleles are neither dominant or recessive They blend to produce a new phenotype.

4. For example, when a red snapdragon is crossed with a white snapdragon, all of the F 1 offspring are an intermediate color – pink.

6. Example A certain type of flower will produce green petals when a blue flower is crossed with a yellow flower. Cross two green flowers. BB = blueYY = yellow BY = green BY x BY B BY Y BBBY YYBY Genotype: 25% = BB 50% = BY 25% = YY Phenotype: 25% = blue 50% = green 25% = yellow

7. Codominance Codominance occurs when both alleles are equally dominant and both are expressed in a new phenotype. If a red cattle is crossed with a white one, the offspring are roan. A roan coat is a mixture of red and white hairs intermingled. Essentially both alleles are dominant.

9. Multiple Alleles For each of the traits that Mendel studied, there were only 2 alleles (ex. round/wrinkled, tall/short, etc.) It is possible to have more than 2 alleles for a trait. Human blood type is an example of a trait that has multiple alleles (A, B, O)

10. Blood Types Type O is recessive Types A and B are dominant to O, but are codominant to each other

11. Blood Type Chart Blood Type (phenotype) Genotype Ooo AAA, Ao BBB, Bo AB

12. Example A woman whose blood type is pure A marries a man whose blood type is O. What are the possible blood types of their children? AA x oo A oo A Ao Genotype: 100% = Ao Phenotype: 100% = type A