Question

A colorblind mother and a normal father give birth to a Klinefelter child with normal vision. Where do you think the non-disjunction has taken place?

(a) 1^st meiotic division of mother

(b) 2^nd meiotic division of the father

(c) 2^nd meiotic division of mother

(d) 1^st meiotic division of father

I have been asked this question in unit test.

My query is from Sex Linked Inheritance in chapter Chromosomes and Sex Determination of Cytogenetics

Answer 1

The correct option is (d) 1^st meiotic division of father

For explanation I would say: The non disjunction must be in the male parent as the child was not color blind. This is possible only if one X chromosome was normal which here came from father. Also as the disjunction produced XY and not two copies of same chromosome it must have been in 1^st division.