Question

If an individual has the chromosomal pattern XXY, in which parent and during which cell division did nondisjunction most likely occur?

A) Nondisjunction in the mother during meiosis I
B) Nondisjunction in the mother during meiosis II
C) Nondisjunction in the father during meiosis I
D) Nondisjunction in the father during meiosis II

Answer 1

Nondisjunction most likely occurred during meiosis I in either the mother or father, resulting in two normal gametes and two gametes with two copies of the X chromosome (XX).

Step-by-step explanation:

Nondisjunction can occur during either meiosis I or meiosis II, with different results. If homologous chromosomes fail to separate during meiosis I, the result is two gametes that lack that particular chromosome and two gametes with two copies of the chromosome. If sister chromatids fail to separate during meiosis II, the result is one gamete that lacks that chromosome, two normal gametes with one copy of the chromosome, and one gamete with two copies of the chromosome.

Therefore, in the case of an individual with the chromosomal pattern XXY, the most likely scenario is that nondisjunction occurred during meiosis I in either the mother or the father, resulting in two normal gametes (XY) and two gametes with two copies of the X chromosome (XX).