Question

Which statement describes the gametes that joined together to form this karyotype?

A. The gametes formed normally, and then one chromosome was added when they joined together.
B. The gametes formed normally, and then one chromosome split apart when they joined together.
C. One gamete formed abnormally because a pair of homologous chromosomes failed to separate.
D. Both gametes formed abnormally because in each gamete, one pair of homologous chromosomes failed to separate.

Answer 1

The karyotype was formed when one gamete, which developed abnormally due to nondisjunction of homologous chromosomes, joined with a normal gamete, leading to a zygote with an abnormal number of chromosomes.

Step-by-step explanation:

The correct statement that describes the gametes which joined to form the karyotype in one gamete formed abnormally because a pair of homologous chromosomes failed to separate. This error in chromosome separation during gamete formation is known as nondisjunction and results in aneuploidy, where the resulting zygote has an abnormal number of chromosomes.

Nondisjunction can occur during either meiosis I or meiosis II. If nondisjunction happens during meiosis I, it results in two gametes with an extra chromosome (n+1) and two gametes with one less chromosome (n-1). Conversely, if nondisjunction occurs during meiosis II, one gamete ends up with an extra chromosome, one gamete lacks that chromosome, and the remaining two gametes are normal. Therefore, if a gamete with an extra chromosome (n+1) joins with a normal gamete (n), the result would be a zygote with an extra chromosome.