Non-Mendelian Genetics 6B Incomplete & Codominance Multiple Alleles

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

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?

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

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:

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:

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

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)

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:

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

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

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.

Blood Types