Part A
Couple 1 comes into your office. The husband has normal vision; the wife is heterozygous for the color-blindness allele.
What percentage of Couple 1’s male offspring will be color blind? What percentage of their female offspring will be color blind?
Part B
Couple 2 comes into your office. The husband is color blind; the wife is homozygous for the normal vision allele.
What percentage of Couple 2’s male and female offspring will be color blind?
Part C
Couple 3 comes into your office. The husband is color blind; the wife is heterozygous for the color-blindness allele.
What percentage of Couple 3’s male and female offspring will be color blind?
Part D
Review the results you obtained for the female offspring of the three couples.
Based on your results for the female offspring, predict whether color blindness is a dominant or recessive trait. Explain your reasoning.
Part E
Complete the Punnett squares below to determine the possible genotypes of each couple’s male and female offspring. (X represents the normal color vision allele. X represents the color-blindness allele. Y represents the Y chromosome, which does not carry the color-vision gene.)
Part F
Review the results you obtained for the female offspring of all three couples. Then, look at the female offspring (the offspring with two X chromosomes) in your three Punnett squares.
What genotype must a female child have in order to be color blind?
Part G
Review the results you obtained for the male offspring of all three couples. Then, look at the male offspring (the offspring with a Y chromosome) in your three Punnett squares.
What genotype must a color-blind male have? Explain.
Part H
Think it over
Explain why color blindness occurs more commonly in males than females.
Part I
Based on your Punnett squares, determine whether a son can inherit color blindness from his father. Explain your reasoning.
