IMAT 2016 Q35 [Meiosis]

In the testes of a healthy man there are diploid cells that undergo meiosis to produce gametes.

Which of the following statements is/are correct about meiosis for one of these diploid cells?

  1. The diploid cell has doubled its DNA content before the start of meiosis I.
  2. The cells at the start of meiosis II are diploid.
  3. The total number of chromosomes produced by the end of meiosis II is double that of the original diploid cell.

A. 3 only
B. 2 and 3 only
C. 1, 2 and 3
D. 1 and 3 only
E. 1 only

The correct answer is D.

What is meiosis?

It is a type of cell division, just like mitosis.

Its purpose is to reduce the number of chromosomes in gametes and, ultimately, to allow sexual reproduction.

Indeed, since we humans have 46 chromosomes (2n = 46), it is not possible for the child to receive 46 chromosomes from both parents.

Furthermore , each diploid cell undergoes 2 rounds of division, and ultimately, yields 4 haploid cells. To make this possible, just before the cell enters meiosis, it duplicates its DNA and therefore, item 1 is correct.

In addition, we know that 1 mother cell yields 4 haploid cells, which means that the total number of chromosomes produced by the end of meiosis II is double that of the original diploid cell. This makes item 3 correct.

The daughter cells are obtained after going through the 4 different phases and 2 different cell divisions :

  • Prophase I and II
  • Metaphase I and II
  • Anaphase I and II
  • Telophase I and II

Therefore, meiosis ends with meiosis II.

We know that the daughter cells at the end of the division are haploid, which makes item 2 incorrect.

A diploid cell has 2 complete sets of chromosomes (2n) and a haploid cell only has 1 set of chromosomes (n)