Meiosis – an interesting cell cycle 25th July 2023 – Tags: , , , , ,

Meeting with articles or scientific books related to biology, we often come across words such as meiosis and mitosis. Both, despite their mysterious name, play a very important role in the life of the cell. Unfortunately, we often confuse them due to similarities in the name and location of the action. Thanks to this article, we will learn what the meiosis process does.

What is meiosis?

The purpose of meiosis is to produce gametes – reproductive cells, sperm and egg cells. Through this process, we obtain daughter cells that contain the same number of chromosomes as the starting cell. During meiosis, a diploid cell, i.e. one with two sets of chromosomes, divides into haploid cells – cells with one set of chromosomes. The germ cells mentioned earlier are haploid cells that during the fertilization process form a diploid cell with a new genome.

What is meiosis
What is meiosis

The photo shows a microscope image showing the different stages of meiosis.

Meiosis stages:

Meiosis can be divided into 9 stages. These stages are further divided into the first cell division (meiosis one) and the second cell division (meiosis two):

First meiosis

Interphase

The DNA in the cell is copied creating two identical sets of chromosomes. Outside the nucleus are two centrosomes, each containing a pair of centrioles. These structures are essential for the cell division process. During interphase, microtubules begin to stretch.

Meiosis
Meiosis

Prophase 1

  • The copied chromosomes join together to form X-shaped structures. Each chromosome consists of two sister chromatids containing identical genetic information. The chromosomes pair up so that both copies of chromosome 1 are linked together, just like the rest of the chromosomes. The formed pairs of chromosomes can exchange pieces of DNA in a process called genetic recombination or crossing over. At the end of prophase one, the membrane surrounding the cell nucleus dissolves, releasing the chromosomes. The meiotic spindle, containing microtubules and other proteins, extends across the cell between the centrioles.

Metaphase 1

  • Pairs of chromosomes line up along the center of the cell. The centrioles are on opposite sides of the cell with the meiotic spindle protruding from them. Meiotic spindle fibers attach to one of each pair of chromosomes.

Anaphase 1

  • The chromosome pairs are then broken apart by the meiotic spindle, which pulls one chromosome to one end of the cell and the other to the other end. During the first meiosis, the sister chromatids stay together.

Telophase 1 and cytokinesis

  • Chromosomes complete their journey to opposite ends of the cell. A complete set of chromosomes accumulates at each end of the cell. A membrane is formed that surrounds each set of chromosomes to create two new nuclei. The single cell then splits in the middle into two sister cells that contain the full set of chromosomes in the nucleus.

Second meiosis

Prophase 2

  • After the completion of the first meiosis, two sister cells are formed, each with 23 chromosomes. In each of the cells, the chromosomes reassemble into X-shaped structures. The membrane surrounding the cell nucleus in each cell dissolves, releasing the chromosomes. The centrioles double. The meiotic spindle forms again.

Metaphase 2

  • In each cell, the chromosomes line up from the beginning to the end of the cell. The centrioles are now at opposite ends of the cell. Spindle fibers at each end of the cell attach to sister chromatids.

Anaphase 2

  • Sister chromatids move away to opposite sides of the cell. The separate chromatids are now individual chromosomes.

Telophase 2 and cytokinesis

  • Chromosomes end their way to opposite ends of the cell. Each end contains a full set of chromosomes. A membrane forms around the set of chromosomes to form the nucleus. This is the final stage of meiosis, although cell division is not fully completed without another round of cytokinesis.

What do we get with meiosis?

When the process is complete, four cells with half the set of chromosomes are produced. In other words, they are haploid. In men, four reproductive cells called sperm are produced. Women produce one egg and three polar bodies (small cells that do not develop into an egg).

The picture shows the importance of meiosis in oogenesis – the formation of egg cells. The formation of the egg cell and polar bodies is visible.

What do we get with meiosis

The picture shows the importance of meiosis in spermatogenesis, i.e. the formation of sperm cells. The formation of four cells is visible.

Meiosis stages
Meiosis stages
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