(B) What do you understand by the terms ‘mitosis’ and meiosis’? Explain giving significance of each.

ANS- Mitosis is the second part of the standard cell cycle. The three cell cycle stages are as follows:

·         Interphase: The stage at which a cell is at for most of its life.

·         Mitosis: At the end of interphase, the cell's DNA gets duplcated. During mitosis, that duplicate DNA gets distributed evenly to to daughter cells.

·         Cytokinesis: When those two daughter cells separate from each other.

In other words, the goal of mitosis is to make sure that when a cell replicates, it gets the same genotype as the parent. Mitosis goes through four stages.

Meiosis needs to create cells with only half the ploidy of the parent cell. Meiosis takes place in two stages: Meiosis I and meiosis II. Here are the steps of meiosis I (simplified as above).

·         Prophase I: Chromosomes form as in mitotic prophase. But then the chromosomes pair up into their homologous pairs, leading to homologous recombination. Between the sister chromosomes, chiasmata form and genetic exchange takes place here. This means that the DNA of the evntual daughter cell is changed, and this is one of the mpost important reasons for the maintenance of sex as a reproductive mode.

·         Metaphase I: As in mitotic metaphase, alignment at the center occurs. But instead of having chromatids being pulled apart by the kinetochores, it's sister chromosomes that get pulled apart.

·         Anaphase I: The chromosomes are pulled to the opposing ends of the cell.

Because there is only one set of chromosomes at each end of the cell, there is only one set of DNA in each daughter cell when cytokinesis takes place. The end result after meiosis I is two haploid daughter cells. Then meiosis II happens, which is almost identical to mitosis, resulting in two more cells.

So the end results of each:
Mitosis: 1 diploid cell -> 2 diploid cells. Goal is cell division.
Meiosis: 1 diploid cell -> 4 haploid cells. Goal is gamete production.