Why does meiosis occur


We will deal with meiosis in this article. We will explain to you what is meant by meiosis and what it is used for. This article belongs to our field of biology or genetics.

During fertilization, the man's sperm fuses with the woman's egg. A fertilized egg is created with the genetic information of both parents. During fertilization, there is a union of the sex cells and thus also the sets of chromosomes. During the development of life, the number of chromosomes must be halved, otherwise the number of chromosomes would double in each generation. The halving process is done through a process called meiosis reached.


Meiosis phases

For a better overview, meiosis is divided into different phases, in which, roughly speaking, one differentiates between a first meiosis and a second meiosis. Before the meiosis, however, there is an interphase in which the chromosomes double. To understand meiosis, one has to know what a chromatid is. So here's a quick definition: A chromatid consists of a double strand of DNA and the associated chromatin proteins. Depending on which cell cycle phase a cell is in, a chromosome consists of one or two chromatids.

First maturity:

The first division consists of prophase 1, metaphase 1, anaphase 1 and telophase 1. The first division serves to separate the chromosomes, which consist of two chromatids.

Prophase 1:

In prophase 1 the chromosomes spiral and can be seen as fine threads under the microscope. The homologous chromosomes begin to stick together closely and in parallel. A tetrad of four chromatids is created. "Contact points" can be seen between the chromatids, at which the chromatids cross one another. This crossing is called the chiasm and is created by crossing over.

The following graphic shows what happens when you cross over:

  1. We have two chromosomes (drawn in red and green), each of which consists of two chromatids.
  2. A chromatid of the chromosome drawn in green overlaps with a chromatid of the chromosome drawn in red.
  3. There are breaks in the chromatids. The chromatid pieces are reassembled "crosswise" at the breakpoints.

Metaphase 1:

In metaphase 1, the nuclear membrane is dissolved. In this phase the homologous chromosomes are arranged on both sides of the equatorial plane and one chromosome each (consisting of two chromatids) points to a spindle pole.

Anaphase 1:

The homologous chromosomes are drawn to the poles by the spindle fibers. The distribution of the male and female chromosome pairs is random.

Telophase 1:

In telophase 1, the cells are constricted with subsequent separation. Two cells with different genetic material are formed. The chromosomes are de-spiralized.

Second maturity division:

The second meiosis consists of prophase 2, metaphase 2, anaphase 2 and telophase 2. The second meiosis is about separating the two sister chromatids. It is similar to mitosis.

Prophase 2:

In prophase 2 the chromosomes become visible again and the spindle apparatus develops. The chromosomes shorten and the nuclear membrane dissolves.

Metaphase 2:

The daughter cells begin to form new nuclear spindle. The chromosomes are arranged in the equatorial plane.

Anaphase 2:

In anaphase 2, the sister chromatids are pulled apart. There is a separation of the chromosomes into two chromatids, which move to the poles.

Telophase 2:

In telophase 2, the two daughter cells of meiosis 1 each create two new daughter cells. A total of four daughter cells were created, all of which only have one haploid chromosome set. Also worth mentioning: A new nuclear membrane is formed in telophase 2.


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