Question

Analyse the events during every stage of cell cycle and notice how the following two parameters change. i) number of chromosomes (N) per cell. (ii) amount of DNA content (C) per cell.

Answer 1

The cell cycle involves a series of events that prepare the cell for division and later cells undergo division. The preparation of cells for the division is called a preparatory stage and is also called interphase. And the division phase is called a mitosis stage and meiosis stage.

Complete answer:
The cell divides and reproduces in two processes mitosis and meiosis. The process of mitosis will give two identical daughter cells whereas the meiosis will result in the four sex cells.
The stages of mitosis are:

Prophase – The genetic material is present as a thin thread-like structure called chromatin. They start to condense to form a chromosome. The nuclear membrane and nucleolus start to disappear.
Metaphase- The chromosomes condense themselves further and two chromatids are held together by a centromere. Chromosomes align themselves in the equatorial. The mitotic spindle fibers are attached to the centromere.
Anaphase- the spindle fibers pull the chromatids to the opposite pole.
Telophase- The chromosomes present at each pole of the cell gather together. There will be a formation of the nuclear membrane and nucleolus. A single cell pinches off and forms two identical daughter cells.

In germ cells, meiosis takes place where one cell will divide and give rise to 4 daughter cells. Stages of meiosis are as follows:
Meiosis I - In meiosis I homologous chromosomes separates into two cells that will give rise to one chromosome per chromosome pair in each daughter cell. The stages of meiosis are as follows
Prophase I- Before this step, the chromosome is replicated to form a sister chromatid. There will be the disintegration of the nuclear membrane and the chromosomes start to condense. At this stage crossing over and exchange of parts of the chromosome takes place.
Metaphase I - The chromosomes align in the equatorial plane and the spindle fibers are attached to the centromere.
Anaphase I - the homologous chromosomes are pulled by the spindle fibers to the opposite pole.
Telophase I and Diakinesis I- There will be a reformation of the nuclear envelope. In Diakinesis I, the cytoplasm and the cell undergoes division.
Meiosis II-
Prophase II- The nuclear envelope disintegrates and the chromosome starts to condense.
Metaphase II- chromosomes align in a single equatorial line. Spindle fibers are attached to the centromere.
Anaphase II- Sister chromatids are pulled towards the opposite pole.
Telophase II- The nuclear membrane is reformed.
Cytokinesis II-
cytoplasm and cell division that produces 2 – non- identical haploid daughter cells.
The parameters that change during the events of the cell cycle are discussed below:
Several chromosomes (N) per cell.
During Anaphase I of Meiosis I of the cell division, the entire homologous chromosome is pulled to the opposite pole by the spindle fibers. The bivalents get reduced into the two sister chromatids and the daughters will receive one chromatid. This makes the cell haploid in nature by reducing the number of chromosomes per cell.

Amount of DNA content (C ) per cell.
During anaphase II of meiosis II, the chromatids separate due to the splitting of the centromere that holds the sister chromatids together. The sister chromatids move to the opposite side of the pole. This will give rise to haploid DNA and a haploid chromosome.

Note:
In mitosis, the daughters formed are identical to each other since there is no crossing over of chromosomes. It occurs to multiply the cells in the case of somatic cells.
Meiosis forms four haploid cells that are non-identical because of crossing over. It gives rise to reproductive cells such as sperm cells.