Meiosis is a more complex process as compared to mitosis. It occurs in the reproductive cells of male and female eukaryotic organisms.
It can be divided into two distinct parts namely 'Meiosis I' and 'Meiosis II'.
The steps involved in meiosis are described below-
1. DNA replicates and the chromatin organizes to form chromosomes.
Each chromosome consists of two identical sister chromatids joined at the centromeres.
2. .The homologous chromosomes line up next to each other and a unique event, called recombination or crossing over, occurs. In this step the homologous chromosomes exchange DNA between adjacent homologous chromatids. (The sister chromatids of any chromosome are no longer identical to each other.)
3. The centrioles move to the poles of the cell and spindle fibers start emerging from them. Nuclear membrane and nucleolus disintegrate.
4. Homologous chromosomes line up along the equatorial plate of the cell.
The orientation of the chromosomes is random resulting in different characteristics among the offsprings. This verifies the law of independent assortment.
5. The ends of the spindle fibers attach to the centromere of each chromosome. The homologous chromosomes move apart from one another, along the spindle fibers, to the opposite ends of the cell.
Each chromosome is still double stranded and has two sister chromatids.
6. The spindle fibers disintegrate and cytokinesis takes place forming two daughter cells.
Each new cell will have only one member of the homologous pair and will thus be haploid.
The second step called Meiosis II is identical to mitosis and the resulting cells retain the same number of chromosomes. (though without their sister chromatids)
7. The spindle fibers redevelop from the poles of the cell.
8. The chromosomes line up along the equator. The ends of the spindle fibers attach to the centromere of each chromosome.
9. The sister chromatids move to the poles of the cell along the spindle fibers.
10. Cytokinesis takes place and four genetically different haploid cells are formed.
The haploid cells thus formed (from both parents), after fertilization, result in the development of a diploid cell called zygote.
It can be divided into two distinct parts namely 'Meiosis I' and 'Meiosis II'.
1. DNA replicates and the chromatin organizes to form chromosomes.
Each chromosome consists of two identical sister chromatids joined at the centromeres.
2. .The homologous chromosomes line up next to each other and a unique event, called recombination or crossing over, occurs. In this step the homologous chromosomes exchange DNA between adjacent homologous chromatids. (The sister chromatids of any chromosome are no longer identical to each other.)
3. The centrioles move to the poles of the cell and spindle fibers start emerging from them. Nuclear membrane and nucleolus disintegrate.
4. Homologous chromosomes line up along the equatorial plate of the cell.
The orientation of the chromosomes is random resulting in different characteristics among the offsprings. This verifies the law of independent assortment.
5. The ends of the spindle fibers attach to the centromere of each chromosome. The homologous chromosomes move apart from one another, along the spindle fibers, to the opposite ends of the cell.
Each chromosome is still double stranded and has two sister chromatids.
6. The spindle fibers disintegrate and cytokinesis takes place forming two daughter cells.
Each new cell will have only one member of the homologous pair and will thus be haploid.
The second step called Meiosis II is identical to mitosis and the resulting cells retain the same number of chromosomes. (though without their sister chromatids)
7. The spindle fibers redevelop from the poles of the cell.
8. The chromosomes line up along the equator. The ends of the spindle fibers attach to the centromere of each chromosome.
9. The sister chromatids move to the poles of the cell along the spindle fibers.
10. Cytokinesis takes place and four genetically different haploid cells are formed.
The haploid cells thus formed (from both parents), after fertilization, result in the development of a diploid cell called zygote.
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