Question

Color-blindness is an X-linked recessive condition. A man with normal vision and a woman who is color-blind have a child with Turner Syndrome. This child has normal vision. Where did the non-disjunction occur?

• In meiosis I of the mother

• In meiosis II of the mother

• In meiosis I of the father

• In meiosis II of the father

• In either meiosis I or II of the mother.

Answer 1

turners syndrome means indivdual has only one X chromosome here mother is colourblind so she can only pass X chromosome with the allele for colourblindness so X chromosome in the child is from the father so non-disjunction happened in the female, non-disjunction in either meiosis I or meiosis II can result in turners syndrome, if non-disjunction happens in Meiosis I, 2 gametes out of 4 lacks X chromosomes and 2 of them will have an extra copy of the X chromosome. If nondisjunction happens in Meiosis II then 2 normal gametes can be formed also one gamete with an extra copy of X chromosome and another with no X chromosomes so the answer is

In either meiosis I or II of the mother