X-Linked and Blood Type Problems
1. A child is blood type O while the mother is blood type A. What are the possible
genotypes and phenotypes of the father? What blood type(s) can the father NOT have?
Blood type A allele = IA
Blood type B allele = IB
Blood type O allele = i
Blood type O genotype = ii
Since the child is blood type O, it must have inherited the i allele from both parents (one from
the mom, and one from the dad). The mother’s blood type is type A. There are two possible
type A genotypes: IAIA and IAi. Since the child inherited i from the mother, the mother’s
genotype must be IAi .
Therefore, the father could have any blood type that would allow the child to receive the i
allele.
Possible father genotypes: IAi, IBi, ii
The father CANNOT BE homozygous recessive for type A or B. He also cannot be IAIB.
2. In flies, the X-linked recessive mutation causes bright-red eyes in contrast to normal,
dominant white eyes. Determine genotypes and phenotypes of the male and female offspring
of a female fly with heterozygous white eyes and a male with bright-red eyes.
White eye allele = XW
Red eye allele = Xw
Genotype of female fly with heterozygous white eyes = XWXw
Genotype of male fly with bright-red eyes = XwY
XW
Xw
Xw
XW Xw
Xw Xw
Y
XW Y
XwY
50% of girls have XWXw genotype and 50% of girls have XwXw
genotype. Therefore, 50% of girls will have white eyes and 50% will
have red eyes.
50% of boys have XWY genotype and 50% of boys have XwY
genotype. Therefore, 50% of boys will have white eyes and 50% will
have red eyes.