1. Non-Mendelian Genetics
6B Incomplete & Codominance
Multiple Alleles

2. Non-Mendelian Genetics
Stop for first section of notes
Begin Incomplete and Codominance Notes
Non-Mendelian

3. If red flower were dominant over white flower, what color would the F1 generation be?
Why are the offspring a different color from either parent?

4. When neither allele is dominant.
Incomplete Dominance: -The heterozygous phenotype (i.e. Rr) is between the two homozygous phenotypes -Neither allele is dominant over another -Example: a red flower crosses with a white flower to make pink flower.
Does not support blending inheritance
Genotype
Phenotype
RR (homozygous)
Red
rr (homozygous)
White
Rr (heterozygous)
Pink

5. Incomplete Dominance Practice Problem
A species of mice are controlled by incomplete dominance. The two alleles are black (B) and white (W). The heterozygous genotype is expressed as gray fur. Give the phenotypes: BB: WW: BW:

6. Incomplete Dominance Practice Problem
Cross a gray male mouse with a white female mouse. List the probabilities of having the following offspring phenotypes: Black: Gray: White:

7. How are these two phenotypes different?
Incomplete dominance
Codominance
Neither allele is expressed (blended)
Both alleles are expressed (mixed)

8. Codominance:
Both alleles are clearly expressed in the phenotype of a heterozygous.
Some chickens:
Allele for black (B) and white (W) feathers are codominant.
Heterozygous chickens are speckled with black and white feathers (erminette)

9. Codominance Practice Problem
A species of chickens are controlled by codominance. The two alleles are black (B) and white (W). The heterozygous genotype is expressed as black and white speckled chickens. Give the phenotypes: BB: WW: BW:

10. Codominance Practice Problem
Cross a speckled male with a speckled female. List the probabilities of having the following offspring phenotypes: Black: Gray: Speckled:

11. Beyond Dominant and Recessive Alleles
There are important exceptions to many of Mendel’s principles
Not all genes show simple patterns of inheritance
Majority of genes have more than 2 alleles
Many important traits are controlled by more than one gene

12. Multiple alleles: genes with more than two alleles
We’ve been working with two alleles (R/r)
Human Blood type has more than two alleles
How many alleles are there? Just three A, B and O. Together, they make four phenotypes.

13. Blood Types