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Frequency of offspring for X linked dominant trait

5. State the distribution (in terms of expected percentages) of eye color among the male and female offspring derived from each of the following crosses considering the following:

In the fruit fly, red eye color "R" is dominant over white eye color "r"; and the gene for eye color is on the X chromosome.

a. White-eyed female and red-eyed male.

b. Heterozygous red-eyed female and red-eyed male.

c. Homozygous red-eyed female and white-eyed male.

d. Heterozygous red-eyed female and white-eyed male.

e. White-eyed female and white-eyed male

Solution Preview

Since males only have one X chromosome the will always only have one eye color allele determining what color eyes they will have.

Females on the other hand have two X chromosomes so their eye color is determined by both alleles. In this case we are told red eye color 'R' is dominant and white eye color 'r' is recessive. So in females the genotypes RR, Rr, rR will be red eyes. Only the rr genotype will have white eyes.
In males R will obviously be red and r white.

In each of these crosses we will always have 50% males and 50% females. Half of the males (25% of total ...

Solution Summary

Calculates expected offspring's eye color frequency in crosses of fruit flies where eye color is on the X chromosome and red eyes R is dominant of white eyes r.