There are two cell divisions takes place during meiosis for the formation of four daughter cells. Meiosis is also called a reduction division in which reduction in chromosome by half results in the formation of four haploid daughter cells.
Further Explanation:
In the process of meiosis, DNA replication involves two cycles of cell division for the formation of four daughter cells, and each chromosome contains half of the chromosomes as their original parent cell. Meiosis is completed in two steps are, meiosis I and meiosis II. Meiosis I and meiosis II involves four steps of cell division:
Meiosis I:
(a) Prophase I: It is the first meiotic division that lasts for a longer period of time as it further classified into five phases based upon its chromosomal behaviour:
Leptotene stage: In this stage, the chromosome can be seen under the compound microscope. This stage involves the compaction of chromosomes.
Zygotene stage: This stage is the second stage of leptotene that involves pairing of chromosomes results in the association of synapsis. The process pairing of a chromosome is called a homologous chromosome. The synapsis formation of the chromosome is influenced by the formation of a structure called the Synaptonemal complex. This complex is formed by the pairing of synapsed homologous chromosomes and is called bivalents or tetrads.
Pachytene stage: In this stage the clear appearance of bivalent chromosomes as tetrads can be seen. It is characterized by the appearance of recombination nodules that serves as the site where crossing over takes place between non-sister chromatids of homologous chromosomes. The process of crossing over also takes place in this stage.
Diplotene stage: This is stage is characterized by the dissolution of the Synaptonemal complex. The X-shaped structures formed are called chiasmata.
Diakinesis: This stage is characterized by the terminalisation of chiasmata. In this stage, the chromosomes are fully condensed.
(b) Metaphase I: In this phase, the bivalent chromosomes are aligned at the equatorial plates. The microtubules from the opposite poles of the spindle are attached to the pair of the homologous chromosome.
(c) Anaphase I: This stage is characterized by the separation of chromosomes whereas the sister chromatids are remains associated at their centromeres.
(d) Telophase I: In this stage, the nuclear membrane and nucleolus reappear. Cytokinesis of cell takes place and is called a diad of cells.
Meiosis II:
Prophase II: This stage of meiosis II occurs just after cytokinesis and usually before the chromosomes become fully elongated. In this stage, the nuclear membrane disappears at the end of prophase II, and the chromosomes again become compact.
Metaphase II: This stage involves the alignment of chromosomes at the equator. The microtubules from the opposite poles of the spindle are get attached with the kinetochores of the sister chromatids.
Anaphase II: This stage starts with the simultaneous splitting of the centromere of each chromosome.
Telophase II: This is the last stage of meiosis in which the chromosomes are enclosed by a nuclear envelope. Cytokinesis is followed by the formation of a tetrad of cells.
Learn more:
Learn more about meiosis
Learn more about the process of molecular diffusion in a cell
Learn more about human sperm and egg cell
Answer Details:
Grade: High School
Subject: Biology
Chapter: Cell cycle and cell division
Keywords:
Cytokinesis, DNA replication, tetrad formation, chromosomes, meiosis I, meiosis II, anaphase II, anaphase I, metaphase I, metaphase II, Zygotene, Leptotene, Pachytene, diakinesis, prophase I, meiosis I.
