How does meiosis reduce chromosome number by half?

Meiosis reduces chromosome number by half through two rounds of cell division, known as meiosis I and meiosis II.

Meiosis is a type of cell division that produces four daughter cells, each with half the number of chromosomes as the parent cell. This process is crucial for sexual reproduction, as it ensures that offspring have the correct number of chromosomes.

In the first round of division, meiosis I, homologous chromosomes pair up and exchange genetic material in a process called crossing over. This is followed by the separation of these homologous pairs, each going to a different daughter cell. This effectively halves the number of chromosomes, as each daughter cell receives only one chromosome from each pair.

The second round of division, meiosis II, is similar to mitosis. The sister chromatids of each chromosome are separated and distributed to different daughter cells. However, unlike mitosis, there is no replication of DNA before meiosis II. This means that the daughter cells have half the number of chromosomes as the original parent cell.

It's important to note that the chromosomes in the daughter cells are not identical to those in the parent cell. This is due to the crossing over that occurs in meiosis I, which shuffles the genetic material and creates new combinations of genes. This genetic variation is a key advantage of sexual reproduction, as it increases the chances of survival in changing environments.

In summary, meiosis reduces the chromosome number by half through two rounds of cell division. In meiosis I, homologous chromosomes are separated, and in meiosis II, sister chromatids are separated. This results in four daughter cells, each with half the number of chromosomes as the parent cell. The process of meiosis also introduces genetic variation, which is beneficial for the survival of species.