[Biology Class Notes] on Stages of Meiosis Pdf for Exam

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. 

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

2. Prometaphase I

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

3. 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. 

4. Anaphase I

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

5. Telophase I and Cytokinesis I

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

Meiosis II

The two cells further undergo division and are termed as equational division. In equational division, chromosome numbers in the daughter cells are not reduced. Moreover, it gains the same number of chromosomes as there are 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

2. Metaphase II

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

3. Anaphase II

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

4. Telophase II

Identical the same stage in meiosis I

5. Cytokinesis II

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

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 into four cells.

Solutions

i. (a) Congression.

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

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Relevance of Meiosis

Meiosis is responsible for the formation of gametes. During meiosis, chromosomes from the parent cells are distributed equally in the cells. Meiosis is responsible for lending diversity in the different species as the unique arrangements of chromosomes result in unique offspring. This causes variation in all species. All students who need to take up biology later on in life to further their career need to know about meiosis.