Question

In Drosophila, an individual female fly was observed to be of the XXY chromosome complement

(normal autosomal complement) and to have white eyes as contrasted with the normal red eye
color of wild type. The female's father had red eyes, and the mother had white eyes. Knowing that
white eyes are X-linked and recessive, present an explanation for the genetic and chromosomal
constitution of the XXY, white-eyed individual.
A) nondisjunction in meiosis II of father
B) nondisjunction in meiosis II of mother
C) nondisjunction in either meiosis I or meiosis II of the mother
D) nondisjunction in meiosis I of mother and meiosis II of father
E) nondisjunction in meiosis I of mother

Answer 1

The white-eyed XXY Drosophila female likely inherited her genetic constitution due to nondisjunction in her mother's meiosis I or II, leading to an egg with two X chromosomes with a white eye allele.

Step-by-step explanation:

In the case of the X-linked white-eyed Drosophila female with an XXY chromosomal complement, we can explain her genetic makeup through nondisjunction occurring in her mother. Since the female has white eyes (which is recessive) and her father had red eyes, the mother must have passed on an X chromosome with the white eye allele. Furthermore, because the female is XXY, there must have been a failure of the X chromosomes to segregate normally during one of the mother's meiotic divisions, leading to an egg with two X chromosomes rather than one. This event is nondisjunction, which could have taken place either in meiosis I or meiosis II, as option C suggests.