Question

A couple has a son with XYY syndrome, a condition in which an extra copy of the Y chromosome is present. This condition also results from nondisjunction. During which meiotic division, and in which parent, could nondisjunction have occurred to produce a child with this condition?Select all that apply. a. Meiosis I in the mother b. Meiosis II in the mother c. Meiosis I in the father d. Meiosis II in the father

Answer 1

Answer:

d. Meiosis II in the father

Explanation:

Since the son has two extra Y chromosomes, the nondisjunction would have occurred in father because females do not have Y chromosome. Before Meiosis DNA replication occurs during which the homologous chromosomes are replicated. During Meiosis I crossing over occurs and homologous chromosomes separate from each other. During Meiosis II sister chromatids of a chromosome separate and move into individual daughter cells.

Here, during Meiosis II the sister chromatids of Y chromosome did not separate from each other (nondisjunction). They collectively moved to one daughter cell. As a result one daughter cell had two Y chromosomes and other daughter cell had none. When the daughter cell containing two Y chromosomes combined with the daughter cell containing one X chromosome from mother, XYY individual was born.