Stages of meiosis

Meiosis is determined by two nuclear divisions rather than the single division seen in mitosis. These two nuclear divisions (meiosis I and meiosis II) have the same names as mitosis, with one exception. Prophase I, prometaphase I, metaphase I, anaphase I, and telophase I are the phases of meiosis I. Prophase II, prometaphase II, and so on are the phases of meiosis two.

Meiosis :

Meiosis is a cell division process in which a single cell divides twice to produce four cells with half the genetic material of the original cell. In males and females, these cells are our sperm and eggs, respectively.

Stages of meiosis:

Meiosis uses a two-step division mechanism to achieve these goals. Homologue pairings separate during meiosis I, the first round of cell division. During a second cycle of meiosis, sister chromatids split.

Meiosis I: prophase I (2N), metaphase I (2N), anaphase I (N+N), and telophase I (N+N)

1)Prophase I

Events that occur during the prophase I of mitosis also appear during prophase I of meiosis. The nuclear membrane coils up, and the chromosomes coil up.

The centrosomes begin to move apart as the centrosomes begin to dissolve.

Crossing-over is a process in which two chromosomes exchange parts .When the chromosomes begin to partially separate in late prophase and continue to separate until they completely split chromosomes that are mixers of the two original chromosomes during anaphase .

2) Metaphase I

Bivalents (tetrads) arrange themselves in the cell’s center and attach themselves to spindle fibers. The random arrangement of pairs of chromosomes is known as independent assortment.

3) Anaphase I

When homologous chromosomes split, Anaphase I starts.

4) Telophase I

Nucleoli reappear when the nuclear envelope reforms.

Meiosis II: prophase II (N+N), metaphase II (N+N), anaphase II (N+N+N+N), and telophase II (N+N+N+N)

1. Prophase II

The centrosomes begin to move apart as the chromosomes coil up and the nuclear membrane begins to dissolve.

2. Metaphase II

Sister chromatids align to the equator of the cell, and spindle fibers develop.

3. Anaphase II

Sister chromatid separation

4. Telophase II & Cytokinesis II

When the chromatids reach the poles, they uncoil, forming thin threadlike chromatin. From two diploid (2n) cells, the nuclear membrane reforms into four daughter cells that are haploid (n).

Explain Zygotene stage?

The stage of meiotic prophase that occurs after the leptotene and during which homologous chromosomes synapse.

Difference Between Meiosis I and Meiosis II:

Homotypic/Heterotypic Division:

Meiosis I is a heterotypic division in which the number of chromosomes in the daughter cell is reduced by half when compared to the parent cell.

Meiosis II is a homotypic division that equalises the number of chromosomes in both the parent and daughter cells.

Chromosomes:

At the start of meiosis I, homologous chromosomes are present.

At the start of meiosis II, individual bivalent chromosomes are present.

Phases:

The four phases of meiosis I are prophase I, metaphase I, anaphase I, and telophase I.

The four phases of meiosis II are prophase II, metaphase II, anaphase II, and telophase II.

Number of Daughter Cells at the End:

In meiosis I, a single parent cell produces two daughter cells.

In meiosis II, the two daughter cells created during meiosis I are split into four cells.

Cross-over:

Chromosomal crossover occurs during prophase I of meiosis, when genetic material is exchanged between non-sister chromatids.

During prophase II of meiosis II, no chromosomal crossover occurs.

Complexity and Time Taken:

Meiosis I is a more complicated division. So, it takes a lot of time.

Meiosis II is a relatively easy process that takes less time to complete.

Conclusion:

Meiosis is the process through which organisms produce gametes during sexual reproduction. Meiosis is divided into two phases: meiosis I and meiosis II. Prophase, metaphase, anaphase, and telophase are the four phases that make up each stage. The law of independent assortment governs the pairing of homologous chromosomes during meiosis I. At chiasmata, chromosomal crossover occurs between non-sister chromatids, resulting in the production of new allele combinations through genetic recombination. At meiosis I, a diploid parent cell’s homologous chromosomes are divided into two haploid daughter cells. Meiosis II is similar to mitotic cell division in that it equalises the amount of chromosomes in the parent and daughter cells created during meiosis I. The fundamental difference between meiosis I and meiosis II is that in meiosis I, genetic recombination occurs, whereas in meiosis II, no DNA recombination occurs.