Question

discuss the big picture of meiosis

Answer 1

Meiosis division occurs in germ cells where a single cell divides twice to produce four cells containing half the number of chromosome to parent cell. These cells are sex cells or gametes which are haploid.

Meiosis can be divided into two phase meiosis 1 and meiosis 2.

Meiosis I

Interphase I:

The DNA replication in the cell resulting in two identical sets of chromosomes. There are two centrosomes present at each pole of the cell, each containing a pair of centrioles which are critical for the process of cell division because, during interphase, microtubules extend from these centrosomes.

Prophase I:

In this stage, chromosomes condense and arranged into X-shaped structures. And each chromosome is composed of two sister chromatids. The chromosomes pair up so that both copies of chromosome remain together. Recombination or crossing over occurs in this stage where the pairs of chromosomes may exchange genetic information. The meiotic spindle, consisting of microtubules extends across the cell between the centrioles.

Metaphase I:

The chromosome pairs line up next to each other along the centre plate of the cell and centrioles remain at opposites poles of the cell with the meiotic spindles extending from them. The meiotic spindle attach to one chromosome of each pair.

Anaphase I:

In this stage the pair of chromosomes pulled apart by spindle fibres, which pulls one chromosome to one pole of the cell and the other chromosome to the opposite pole. In meiosis I the sister chromatids stay together which is different from meiosis 2 where sister chromatid gets separated.

Telophase I:

At each opposite pole of the cell, a full set of chromosomes gather together and a membrane forms around each set of chromosomes to create two new nuclei. During cytokinesis, the single-cell then pinches in the middle to form two separate daughter cells each containing a full set of chromosomes within a nucleus.

Meiosis II

Meiosis 2 is also similar to the first one but some stages make it different from meiosis 1.

Prophase II:

Similar to meiosis 1 in each of the two daughter cells the chromosomes condense again into visible X-shaped structure and the meiotic spindle forms again.

Metaphase II:

In each of the two daughter cells, the chromosomes arrange at the center plate of the cell. The centrioles arrange at opposites poles in each of the daughter cells. Meiotic spindle fibres at each pole of the cell attach to each of the sister chromatids.

Anaphase II:

The sister chromatids are then pulled to opposite poles with the help of meiotic spindle. The separated chromatids are now called individual chromosomes.

Telophase II:

At each pole of the cell, a full set of chromosomes gather together where a membrane forms around each set of chromosomes to create two new cell nuclei. After this stage cell undergoes another round of cytokinesis. Once cytokinesis is complete there are four cells, each with haploid set of chromosomes.