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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
Reasons for incomplete penetrance Epistatic genes, pleiotropic genes or
other genes which suppress the expression of the genotype
Expressivity in beagles Each of these dogs has
the dominant allele for piebald (black and white) spotting
The degree of spotting varies among individuals