During pregnancy, a cell undergoes what appears to be a normal mitotic nuclear division. However, two daughter cells with 2n-1 and 2n+1 complement of chromosomes are produced, causing a population of cells to be abnormal. Which of the following events is most likely responsible for this disorder?

a. The cleavage furrow did not completely separate the two daughter cells.

b. Homologous chromosomes were sorted incorrectly during prophase.

c. Two sister chromatids did not separate into the proper daughter cells during anaphase.

d. The protein structure of nonkinetochore microtubules was defective, and incorrectly shortened during anaphase.

c. Two sister chromatids did not separate into the proper daughter cells during anaphase.

Explanation:

The observed cell is undergoing mitosis which does not include separation of homologous chromosomes. During anaphase of mitosis, two sister chromatids of each chromosome separate from each other. They move to opposite poles. This results in equal distribution of two complete sets of chromosomes to each daughter cell.

However, the failure of two sister chromatids of a chromosome during anaphase would lead to the formation of two abnormal daughter cells. One of the daughter cells would have one extra chromosome (2n+1) while the other would lack one chromosome from the diploid set (2n-1).