Problems on Sex-related Inheritance

Sex-linked inheritance

1. Illustrate the following crosses among fruit flies and determine genotype and phenotypes of the resulting offspring:
a. true-breeding red-eyed female x white-eyed male
b. heterozygous red-eyed female x white-eyed male
c. white-eyed female x red-eyed male

2. Red- green colorblindness is caused by an X-linked recessive allele. A colorblind man marries a woman with normal vision whose father was colorblind.
a. What is the probability that their daughter will be colorblind?
b. What is the probability that they will have a colorblind son?

3. A man with hemophilia has a daughter of normal phenotype. She marries a man who is normal for the trait.
a. What is the probability that a daughter of this mating will be a hemophiliac?
b. That a son will be a hemophiliac?

4. Given that hypophosphatemia is an X-linked dominant trait. Predict the results of the mating between:
a. An unaffected father and an affected mother
b. An affected father and an unaffected mother

Sex-limited inheritance

5. In domestic fowl, the differences in plumage between males and females is sex-influenced. If the genotypes and phenotypes for plumage are as listed below:

Genotype Female Male
HH hen-feathered hen-feathered
Hh hen-feathered hen-feathered
hh hen-feathered rooster-feathered

Predict the F1 and F2 results of crossing a male that is rooster-feathered and a true-breeding hen-feathered female.

6. In the clover butterfly, all males are yellow, but females may be yellow if they are of the homozygous recessive phenotype (yy) or white if they possess the dominant allele (Y_). What phenotypic proportions are expected from a cross between heterozygous parents?

Sex-influenced inheritance

7. Spotting in cattle is controlled by two alleles where CM is the allele for mahogany and white, while CR is the allele for red and white. This trait is sex-influenced and the different sexes exhibit the two phenotypes as follows:

In males:
mahogany & white à dominant (CMCM, CMCR)
red & white à recessive (CRCR)
In females:
red & white à dominant (CRCR, CMCR)
mahogany & white à (CMCM)

a. If a red & white male is crossed to a mahogany & white female, what phenotypic and genotypic proportions are expected in the F1 and F2 generations?
b. If a mahogany & white cow gives birth to a red & white calf, what sex is the calf?