Question

Analyse the events during every stage of cell cycle and notice how the following two parameters change.

1. Number of chromosomes (N) per cell
2. Amount of DNA content (C) per cell

Answer 1

During meiosis, the number of chromosomes and the amount of DNA in a cell change.

1. Number of chromosomes (N) per cell
   1. The cell is metabolically active in the G₁ phase of interphase. It continues to increase continuously. DNA replication occurs in the S phase.
   2. As a result, the amount of DNA doubles. If the initial amount of DNA is expressed as 2C, then its amount becomes 4C, while there is no change in the number of chromosomes.
   3. If the number of chromosomes in the G₁ phase is 2N, then even in the G₂ phase, their number remains 2N.
2. Amount of DNA content (C) per cell
   1. During anaphase II of the meiotic cycle, the chromatids separate as a result of the splitting of the centromere.
   2. It is the centromere that holds together the sister chromatids of each chromosome. As a result, the chromatids move towards their respective poles.
   3. Therefore, at each pole, a haploid number of chromosomes and a haploid amount of DNA are present.
   4. During mitosis, the number of chromosomes remains the same.
   5. The DNA duplicated in the S phase gets separated in the two daughter cells during anaphase. As a result, the DNA content (C) of the two newly-formed daughter cells remains the same.