MEIOSIS

Theodar Boveri in the year 1880 discovered the meiosis cell division in WARM ASCHAIS and SEA ARCHIN.

This is a very interesting mind twisting cell division in which the single cell divides to produce four cells containing half the actual amount of genetic material.

It is mind twisting also because it occurs twice. In the first phase the cell gets divided into 2 cells and in the second phase both the cell gets divided into four respectively.

Meiosis occurs twice:

• MEIOSIS I
• MEIOSIS II

Till the interphase everything is same as that of mitosis.

Interphase

MEIOSIS I :

• PROPHASE I
• METAPHASE I
• ANAPHASE I
• TELOPHASE I

Meiosis I is very different from mitosis, there are some additional terminologies and additional steps which is done by the cell in the process of meiosis cell division.

PROPHASE I : 

Now in prophase I the chromatin material starts to condense and form chromosomes, the nuclear membrane dissolves and the nucleolus disappears. The centrioles duplicates and the spindle starts to form again.During prophase after chromosome formation there can be a process of recombination or crossing over in which the chromosomes exchanges a bit of DNA with each other.

METAPHASE I :

All the chromosomes align at the equator of the cell and the micotubules of the spindle fiber gets attached to it. 

ANAPHASE I : 

During anaphase the sister chromatids are not separated with each other which is very different from meiosis II and mitosis. The spindle fiber pulls one chromosome to one pole of the cell and the next chromosome to other.

TELOPHASE I : 
In telophase I cleavage furrow appears, nuclear membrane starts to reappear, all the cell organelles appears, chromatids start to decoil and form chromatin material.

CYTOKINESES :

After the process of cytokinesis the two daughter cells separated contains full set of chromosomes within the nucleus, which is very different from meiosis II and mitosis.

Chromatin condenses and forms chromosomes, later crossing over takes place and the cell gets divided into two daughter cells. 

MEIOSIS II : 

• PROPHASE II
• METAPHASE II
• ANAPHASE II
• TELOPHASE II

NOTE*:

More or less everything is same, actually meiosis II resembles with mitosis.

PROPHASE II : 

After cytokinesis there is 23 chromosomes present in each cell. Now in prophase II the chromatin material starts to condense and form chromosomes, the nuclear membrane dissolves and the nucleolus disappears. The centrioles duplicates and the spindle starts to form again.

METAPHASE II :

All the chromosomes align at the equator of the cell and the micotubules of the spindle fiber gets attached to it. 

ANAPHASE II : 

The sister chromatids are the pulled to the ends of the cell. The separated chromatids are now individual chromosomes.

TELOPHASE II : 
In telophase II cleavage furrow appears, nuclear membrane starts to reappear, all the cell organelles appears, chromatids start to decoil and form chromatin material.

CYTOKINESES :

In this the cells get divided with half the actual amount of genetic information and forms gametes.

The final stage, here the sister chromatids splits and go to there individual cells
and forms gametes.