Parentalgeneration X

F1 generation

F2 generation

Nu

mb

er o

f ea

chp

hen

oty

pe

Phenotypes

1

6

1520

15

6

1

Figure 10.20a

Kernel color is quantitative trait.

aa bb cc(pure line white)

X AA BB CC(pure line red)

Aa Bb Cc(medium red)

Self-fertilization

202 AABbcc

2 AaBBcc

8 AaBbCc2 aaBbCC2 aaBBCc2 AabbCC

2 AAbbCc15

4 AABbCc

4 AaBBCc1 aaBBCC4 AaBbCC1 AAbbCC

1 AABBcc

2 AABbCC2 AaBBCC2 AABBCc6

1 AABBCC

15

4 AaBbcc

4 aaBbCc1 aabbCC4 AabbCc1 aaBBcc

1 AAbbcc

2 aabbCc2 aaBbcc2 Aabbcc6

1 aabbcc1

0 1 2 3 4 5 6

Number of red pigment alleles (A, B, or C) in genotype

1

Figure 10.20b

Model to explain inheritance

of kernel color

Predict the phenotype frequencies of a cross between AaBb x Aabb Assume the A locus and B locus are on

different chromosomes

Two genes, each with two alleles, are known to influence coat color in Labrador retrievers. Let’s call the alleles for the first gene B and b and E and e for the second gene. The ratio of colors is 9 black: 3 chocolate: 4 yellow.

1. Suggest a mechanism for inheritance of coat color

2. Write out all possible genotypes and describe the phenotype of each genotype.

Penetrance

The percentage of individuals with a given genotype who exhibit the phenotype associated with that genotype

Pedigree showing incomplete penetrance

Reasons for incomplete penetrance Epistatic genes, pleiotropic genes or

other genes which suppress the expression of the genotype

Expressivity

The degree to which a genotype is expressed in the phenotype

Expressivity in beagles Each of these dogs has

the dominant allele for piebald (black and white) spotting

The degree of spotting varies among individuals

Polydactyly

Penetrance and expressivity

Environmental effects on fur color in Himalayan rabbits

Fur color in Siamese cats