Question

7. A colorblind woman and a man with normal vision have a son with Klineflter syndrome (XXY) who has normal vision. Determine the parent in whom nondisjuction occurs, and whether nondisjuction takes place in the first of second meiotic division. Colorblindness is an X-linked recessive trait.

a. female meiosis I

b. Either male meiosis I or II.

c. male meiosis II

d. female meiosis II

e. male meiosis I

Answer 1

option d) female meosis II

Reason: it is mentioned the patient suffered from Klinefelter syndrome (XXY), so that means that both X chomosomes have to carry the the gene or allele which is responsible for colorblindness. so, nondisjuction must have occured in the female parent or the mother.

during the phase of meiosis I, if there is no crossover occuring inbetween the centromere of the chromosome and the gene, alternative alleles tend to separate. But, incase of meiosis II, seperation occurs between alleles on sister chromatids which are identical. so, the event of nondisjunction must have must have taken place while meiosis II, as during this phase both alleles which are seperated are identical to eachother.