Stages of Meiosis

Definition:

Meiosis is the process in which one cell undergoes division two times for the production of four cells containing half the original quantity of the genetic information. These newly formed cells are sex cells, that is, eggs in females and sperm in males. 

It is the method of gamete formation in which a 4n cell is divided into four different haploid daughter gametes that are non-identical. The daughter gametes are haploid (n) in nature. 

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Do You Know?

Meiosis is extremely important as that creates the correct number of chromosomes in the course of sexual reproduction. Genetic variation is ensured in the recombination process. Such variation is further enhanced with the unification of gametes in fertilisation. The constant combination of parental DNA in case of sexual reproduction has led to today’s incredible diversity in organisms on Earth.  

To understand what is meiosis, let us take a look at its different stages. 

There are 6 stages of meiosis into every cell division – Prophase, Prometaphase, Metaphase, Anaphase, Telophase and Cytokinesis. 

Meiosis I 

Meiosis I is the initial round of nuclear division, which is also called reduction division. It is because resulting cells retain only half of the chromosomes as compared to the parent cell. 

  1. Prophase 1

It involves disintegration of the nuclear envelope and condensation of chromosomes. On chromosome division, spindle fibre appears. 

  1. Prometaphase I

Chromosomes and spindle fibres are attached, and the points of attachment are called centromeres. Here, condensation of chromosomes continues. 

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  1. Metaphase I

The paternal and maternal chromosomes, which are held as homologous chromosomes, randomly align along the equator of the cell. This random assortment is the cause of genetic diversity within offspring. 

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  1. Anaphase I

The homologous chromosomes migrate towards the opposite poles of the cell, and spindle fibre retracts for subsequent DNA division.

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  1. Telophase I and Cytokinesis I

The nuclear envelope modifies leading to disappearance of spindle fibres in telophase I. Two non-identical diploid (2n) daughter cells emerge from cell division in cytokinesis I. 

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Meiosis II

The two cells further undergoes division and termed as equational division. In equational division, chromosome numbers in the daughter cells are not reduced. Moreover, it gains same number of chromosomes as there in the "parent cell" which entered into meiosis II. 

  1. Prophase II and Prometaphase II

[Identical to the same stages in meiosis I and what is meiosis definition]

  1. Metaphase II

Along the cell equator, chromosomes are lined up in a single file. 

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  1. Anaphase II

After splitting of chromosomes, the produced sister chromatids are stretched to opposite poles of equator.

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  1. Telophase II

[Identical to the same stage in meiosis I]

  1. Cytokinesis II

Two non-identical haploid daughter cells are produced on cytoplasm and cell division. As it concurrently takes place in two cells, for identical haploid daughter cells emerge.

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Test Your Knowledge 

i. Which of the following relates to chromosome movement in Metaphase?

(a) Congression.

(b) Repulsion.

(c) Equalisation. 

(d) Polarisation. 

ii. Which of the following takes place in Anaphase 1 stage?

(a) Centromere is first to separate. 

(b) Chromatids separate towards one pole. 

(c) Each homologue moves towards the opposite pole. 

(d) Chromosomes separate to four cells.

[Solutions]

i. (a) Congression.

ii. (c) Each homologue moves towards the opposite pole.

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FAQ (Frequently Asked Questions)

1. Which are the Stages of Meiosis in Order?

Ans. Across meiosis I and II, the order of stages is – Prophase, Prometaphase, Metaphase, Anaphase, Telophase and Cytokinesis. 

2. What is the Number of Times of Cell Division in Meiosis?

Ans. In meiosis, one cell divides twice leading to four cells. These four cells include half of the original genetic information. Daughter cells are formed when a single cell divides twice during meiosis. 

3. Which Cells are Generated After Meiosis?

Ans. After meiosis, haploid daughter cells are produced with differing sets of chromosomal combinations from the parent chromosomes. Four haploid gametes are created in sperm cells.