Stages of Meiosis Simple Notes
Definition
of Meiosis: A type of cell division that produces four haploid cells with half the
number of chromosomes from a diploid parent cell.
You can watch our 4 minute video here Stages of Meiosis
You can watch our 3 minute video here Stages of mitosis
Functions of Meiosis
- Essential for sexual reproduction: Meiosis reduces the chromosome number by half, creating four haploid cells from one diploid cell, essential for sexual reproduction.
- Formation of Gametes: Meiosis produces gametes (sperm and eggs in animals, pollen and ovules in plants) that are necessary for fertilization.
- Genetic Variation: Meiosis generates genetic variation through crossing over and independent assortment which is crucial for evolution and adaptation.
Meiosis is divided into 2 major stages Meiosis I and
Meiosis II
- In Meiosis I: A parent diploid cell forms 2 haploid cells
- In Meiosis II: 2 haploid cell forms 4 haploid cells; just like mitosis
Meiosis
I is divided into 4 substages; Prophase I, Metaphase I, Anaphase I and Telophase
I
Prophase
I
Chromosomes condenses
and become visible
- Homologous chromosomes* pair up (synapsis), forming tetrads (homologous chromosome pair has 4 chromatids; so, called tetrads.)
- Crossing over occurs; it is the exchange of segments between homologous chromosomes that lead to genetic variation.
- Nuclear envelope breaks down and spindle fibers form
Metaphase
I
- The nucleus disappears.
- Tetrads or homologous chromosomes align at the metaphase plate or at the center
- Spindle fibers attach to the centromeres of homologous chromosomes
Anaphase I
- The homologous
chromosomes are pulled apart at the centromere and move
toward opposite poles of the cell.
- Spindle fibres begin to shorten.
- This separation ensures that each new daughter cell will receive half the set of chromosomes of the parent cell
Telophase
I
- Chromosomes arrive at opposite poles and begin to decondense back into chromatin
- Nuclear envelopes begin to reform around each set of chromosomes
- The spindle fibres break down.
- During cytokinesis, the cytoplasm divides, resulting in two separate daughter cells, with chromosome number reduced to half.
Why
is Meiosis I called as reduction division?
From
a diploid parent cell; 2 haploid cells are formed (chromosome number reduced to
half) in Meiosis I; so, called as reduction division
Meiosis
II is divided into 4 substages; Prophase II, Metaphase II, Anaphase II and Telophase
II
Prophase
II
- Chromosomes condenses and become visible again in each haploid cell
- Nuclear envelope breaks down and spindle fibers form
Metaphase
II
- The nucleus disappears.
- Chromosomes align at the metaphase plate or at the center
- Spindle fibers attach to the centromeres of the chromosomes
Anaphase II
- The sister chromatids are
pulled apart at the centromere and move toward opposite poles of the cell.
- Spindle fibres begin to shorten.
Telophase
II
- Chromatids arrive at opposite poles and begin to decondense back into chromatin
- Nuclear envelopes begin to reform around each set of chromosomes
- The spindle fibres break down.
- During
cytokinesis, the cytoplasm divides, resulting in four genetically unique haploid cells
Why
is Meiosis II called as equational division?
From
2 parent haploid cell; 4 haploid cells are formed with same chromosome number
just like mitosis; so, called as equational division.
Suggest Content: Stages of Mitosis Simple Summary notes
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