The Meiosis

What happens during meiosis?

If you look at the karyogram of an egg or sperm cell, you can see that they consist of only 23 chromosomes. All other human cells, e.g. Skin cells, on the other hand, consist of 46 chromosomes. There is a special reason for this: fusion of the egg and the somatic cell also leads to a fusion of the set of chromosomes. The fertilized egg cell (so-called zygote) then again has a diploid (double) set of chromosomes. Germ cells, including sperm and egg cells, have only one haploid (simple) set of chromosomes.

Meiosis (Greek meiono = decrease) is responsible for the halving of the diploid, a haploid chromosome set in germ cells. Were it not for this reduction, the number of chromosomes in fertilization would add up again and again and there would be an almost infinite number of sets of chromosomes. These resulting zygotes would not be viable.

The phases of meiosis

Meiosis I - reduction division

In meiosis I, the homologous chromosomes are separated from each other. From a diploid mother cell thus become two haploid daughter cells. A distinction is made between the following phases:

 Prophase I : The Prophase is divided into Leptotän, Zygotän, Pachytän, Diplotän and Diakinese. Overall, however, the following events can be summarized: maternal chromosomes attach themselves to homologous paternal chromosomes. This can lead to intrachromosomal recombination (crossing over) between non-sister chromatids. Finally, at the end of the prophase, the core shell dissolves.

 Metaphase I : In metaphase I, the homologous chromosomes are arranged in the equatorial plane. In addition, the spindle apparatus forms at the cell poles.

 Anaphase I : The homologous chromosome pairs are pulled by the spindle fiber devices to the poles. In contrast to mitosis, however, whole chromosomes are pulled to the poles, not single chromatid strands. This distribution occurs randomly and, in addition to the crossing over, ensures additional mixing of the genome.

 Telophase I : The two cells formed separate from each other. Two haploid daughter cells have emerged.

Meiosis II - Equation of Equation

Meiosis II with its phases Prophase II, Metaphase II, Anaphase II and Telophase II basically works just like mitosis, but with the subtle difference that at the end there is a haploid set of chromosomes. Due to meiosis I, which has already produced two daughter cells from one cell, there are four haploid daughter cells at the end of meiosis II (see figure above).

Summary

Meiosis halves the number of chromosomes. This is necessary for the germ cells (sperm and egg cells), because at fertilization the chromosome sets merge together.

Meiosis can be divided into meiosis I and meiosis II. At the end of these two processes, a diploid mother cell produces four haploid daughter cells