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MEIOSIS
The process where a single cell divides twice to produce four cells containing half the original amount of genetic information is called meiosis.
Sperms and eggs are produced by meiosis in animals.
Spores are produced by meiosis in plants.
The Stages of Meiosis
Meiosis is a continuous process. It can be described most easily by dividing it into two arbitrary stages:
Meiosis I
Meiosis II
The First Meiotic Division
It consists of:
Interphase I
Prophase I
Metaphase I
Anaphase I
Telophase I and Cytokinesis
Interphase I
The DNA in the cell is copied, resulting in two identical full sets of chromosomes.
Two centrosomes are present outside the nucleus, each containing a pair of centrioles.
Microtubules extend from the centrosomes.

Prophase I
It is the lengthy process of meiosis.
Each chromosome has two chromatids.
Chromosomes appear as interweaving threads due to chromatin condensation.
Chromosomes become shorter and thicker as condensation proceeds.
Homologous chromosomes begin to pair through a process called synapsis.
The paired chromosomes, called tetrads, consist of four chromatids.
Chiasma forms where chromatids cross each other, and crossing over (exchange of chromosome segments) occurs.
Metaphase I
The nuclear membrane disintegrates.
Microtubules form the spindle apparatus.
Chromosomes line up in a double row along the equator.


Microtubules attach to the kinetochores of homologous chromosomes.
Anaphase I
spindle fibers attached to homologous chromosomes shorten.
Homologous chromosomes are pulled to opposite poles of the cell.
Telophase I and Cytokinesis
Chromosomes complete their movement to opposite poles.
Nuclear membranes form around each set of chromosomes.
Cytokinesis divides the cell into two haploid daughter cells.
The Second Meiotic Division
Meiosis II is similar to mitosis and occurs to separate the sister chromatids.
Interphase II
DNA does not duplicate.
This is a brief phase, and the two cells quickly enter Meiosis II.
Prophase II
No complicated nuclear events occur in this stage.

Metaphase II and Anaphase II
Chromosomes line up as in
Metaphase I.
The centromere divides, and chromatids separate.
Chromatids, now called chromosome, are distributed equally to each pole.
Telophase II
Nuclei are reconstructed with a haploid set of chromosomes in each daughter cell.
DNA has duplicated only once during the entire meiotic process.
Significance of Meiosis
1. Reduction of Chromosome Number:
The number of chromosomes is halved in gametes, ensuring the chromosome number remains constant from generation to generation.
2. Transmission of Genetic Material:
Meiosis provides a mechanism for the transmission of genetic material from one generation to the next
3. Genetic Variability:
It introduces genetic variability through processes like crossing over, leading to unique genetic combinations.
4. Adaptation and Survival:
Meiosis offers a chance for the production of better-adapted individuals, increasing their survival chances in a changing environment.
5. Raw Material for Evolution:
By generating genetic diversity, meiosis provides the raw material for evolution.