A biologist marked a cell that he knew was about to undergo meiosis. A short time later he observed the four cells produced by the original marked cell; their chromosome numbers were 17, 17, 18, and 16. He knew these numbers indicated that something abnormal had occurred during meiosis. Which of the following most likely occurred?

What are the following? Is the below one of the choices?

NONDISJUNCTION: when 2 homologous chromosomes move to the same pole during meiosis. One daughter cell will be missing one chromosome while the other will have an extra chromosome.

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To identify what abnormality occurred during meiosis based on the given information, we need to understand the normal chromosome behavior during meiosis.

During meiosis, the chromosome number is usually halved in order to produce haploid cells (cells with half the number of chromosomes as compared to the parent cell). This reduction in chromosome number occurs through two consecutive cell divisions known as meiosis I and meiosis II.

In meiosis I, homologous pairs of chromosomes separate, resulting in two daughter cells with a haploid number of chromosomes. In meiosis II, the sister chromatids of each chromosome separate, resulting in four daughter cells, each possessing a haploid number of chromosomes.

Based on the information provided (chromosome numbers: 17, 17, 18, and 16), we can deduce that there was an abnormality in the segregation of chromosomes during meiosis I. Normally, the chromosome numbers in the resulting daughter cells after meiosis I should be halved.

In this case, there are two daughter cells with a chromosome number of 17, which suggests that both homologous chromosomes failed to separate during meiosis I. This condition is called nondisjunction, and it can result in aneuploidy, an abnormal number of chromosomes in the daughter cells.

Therefore, the most likely abnormality that occurred during meiosis is nondisjunction of one pair of homologous chromosomes, leading to the unequal distribution of chromosomes into the daughter cells.