Between the two divisions of meiosis, there is:
a) a full cell cycle
b) a pairing of homologues
c) replication of some parts of the chromosomes
d) no S phase
e) random combination among chromatids
The correct answer and explanation is:
The correct answer is d) no S phase.
Meiosis consists of two divisions: meiosis I and meiosis II. The first division, meiosis I, involves the separation of homologous chromosomes into different cells. The second division, meiosis II, is similar to mitosis and separates the sister chromatids of each chromosome.
The key point here is that there is no S phase between meiosis I and meiosis II. In the S phase of the cell cycle, DNA replication occurs to duplicate the chromosomes. However, after meiosis I, the chromosomes do not replicate again before meiosis II. This ensures that the number of chromosomes is halved, a key feature of meiosis, so that gametes (sperm or egg cells) contain half the chromosome number of the original cell.
During meiosis I, homologous chromosomes pair up, undergo recombination (crossing-over), and then are separated into different cells. This process involves pairing of homologues (option b), which leads to genetic diversity in the offspring. But, once meiosis I is complete, there is no additional DNA replication before the second division.
The absence of the S phase between the divisions ensures that when the two sister chromatids separate during meiosis II, the resulting gametes have the correct number of chromosomes, which is half of the original diploid cell. If replication occurred again, it would double the chromosome number, leading to errors in the number of chromosomes in the gametes.
Therefore, the answer is d) no S phase, as there is no DNA replication between the two divisions of meiosis.