In humans, XO individuals are females with Turner syndrome and XXY individuals are males with Klinefelter syndrome.Red green color blindness is caused by an X-linked recessive allele.Suppose a colorblind man and a normal woman with no family history of color blindness married and had a daughter who was colorblind and had Turner syndrome.Which event could have given rise to this offspring?
A)nondisjunction at meiosis I in the mother
B)nondisjunction at meiosis II in the mother
C)nondisjunction at meiosis I in the father
D)nondisjunction at meiosis II in the father
E)nondisjunction at either meiosis I or meiosis II in the mother

Question

Quizplus · Accepted Answer

Since the mother has no family history of color blindness, we know she is not a carrier for the colorblindness allele. Therefore, the daughter must have inherited the colorblindness allele from her father. Since this is an X-linked recessive allele, the daughter must have received the colorblindness allele on her father's X chromosome. The fact that the daughter has Turner syndrome also indicates that she has only one X chromosome, which she must have received from her mother. Therefore, the father must have had an XXY genotype, and his nondisjunction during meiosis would have resulted in the daughter receiving only one X chromosome, which happened to carry the colorblindness allele. The nondisjunction in the mother would have resulted in a different genetic outcome, such as a daughter with Klinefelter syndrome and normal color vision. Therefore, the best answer is E, nondisjunction at either meiosis I or meiosis II in the mother.

In Humans, XO Individuals Are Females with Turner Syndrome and XXY