Question

What is the site of meiosis in an organisms?

Answer 1

Meiosis:

1. Meiosis is a specialized and complicated process where a diploid cell divides twice to produce four cells containing half the original amount of genetic information.
2. These cells are our reproductive cells of gonads – sperm in males, eggs in females.
3. Meiosis comprises of two successive division:

1. Meiosis-I Division ii. Meiosis-II Division

Meiosis-I: - It is divided into four phases:

1. Prophase-I:

• Chromosome composed of two sister chromatids begins to condense and also pair up.
• Each chromosome carefully aligns with its homologue pair.
• The pairs of chromosomes may then exchange bits of DNA in a process called recombination or crossing over.
• Nuclear membrane dissolves away, releasing the chromosomes.
• The meiotic spindle, consisting of microtubules and other proteins, extends across the cell between the centrioles.

2. Metaphase-I:

• The chromosome pairs line up next to each other along the centre (equator) of the cell.
• The centrioles are now at opposites poles of the cell with the meiotic spindles extending from them.

3. Anaphase-I:

• In anaphase I, the homologues are pulled apart and move apart to opposite ends of the cell.
• However, the sister chromatids of each chromosome remain attached to one another .

4. Telophase-I:

• The chromosomes completely arrive at the opposite poles of the cell.
• At each pole of the cell a full set of chromosomes gather together. A membrane forms around each set of chromosomes to create two new nuclei.
• Nuclear envelope around the daughter nuclei and nucleolus also reappears.
• Telophase-I is generally followed by cytokinesis to form two haploid daughter cells.

Meiosis-II: - It is divided again into four phases:

• Cells move from meiosis I to meiosis II without copying their DNA.
• Meiosos-II is similar to mitosis, these cells are haploid have just one chromosome from each homologue pair but their chromosomes still consist of two sister chromatids.
• In meiosis II, the sister chromatids separate, making haploid cells with non-duplicated chromosomes.

1. Prophase-II:

• Sister chromatids of chromosomes begin to condense.
• Nuclear envelope and nucleolus breakdown, the centrosomes move apart, the spindle forms between them.

2. Metaphase-II:

• The haploid number of chromosomes become arranged at the equatorial plate of the spindle.
• Each chromosome gets attached to the spindle fibres by centromere.

3. Anaphase-II:

• The centromere divides and the sister chromatids separate and are pulled towards opposite poles of the cell.

4. Telophase-II:

• Nuclear membranes form around each set of chromosomes, and the chromosomes decondense.
• Cytokinesis splits the chromosome sets into new cells, forming the final products of meiosis: four haploid cells in which each chromosome has just one chromatid.