Meiosis It is one of the ways of cell reproduction. This process is performed in the cells in the sex cells. It is a process of cell division in which a diploid cell (2n) undergoes two successive divisions, with the ability to generate four haploid cells (n). This process is carried out in two nuclear and cytoplasmic divisions, called first and second meiotic division or simply meiosis I and meiosis II
Explanation:
Phases of Meiosis
Two successive cell divisions occur in meiosis, Meiosis I (Reduction) and Meiosis II (Division). Meiosis produces 4 haploid cells. Meiosis is also known as reduction division.
In Meiosis I, the level of ploidy is reduced from 2n to n while in Meiosis II the "set" of remaining chromosomes is divided into a process similar to mitosis (division). The biggest difference in the process occurs during Meiosis I.
- MEIOSIS I: Prophase I
During mating, a key event occurs in the matching of homologous chromosomes.
- Metaphase I
In Metaphase I the tetrads line the equator of the cell. The spindle fibers "stick" to the centromere of each homologous pair and subsequent events are similar to mitosis.
- Anaphase I
During Anaphase I the tetrads separate and the chromosomes are dragged to the opposite poles by the spindle fibers. The centromeres in Anaphase I remain intact.
- Telophase I
Telophase I is similar to mitosis, except that in the end each "cell" has only one group of replicated chromosomes. Depending on the species, the new nuclear membrane can be formed (or not). Some animals can divide their centrioles during this phase.
Telophase may be absent in some species. If there is, it is followed by an interface called interkinesis; Unlike the mitotic interface, there is no duplication of genetic material since each chromosome already has two chromatids. The other difference is that these sister chromatids are no longer genetically identical, due to the cross-linking phenomenon.
- MEIOSIS II: Profase II
During Prophase II, the nuclear membrane (if formed during Telophase I) dissolves, and the spindle fibers appear, as in the prophase of mitosis. Actually, Meiosis II is very similar to mitosis.
- Metaphase II
Metaphase II is similar to that of mitosis, with chromosomes in the equatorial plane and spindle fibers sticking to the opposite faces of the centromere in the kinetochore region.
- Anaphase II
During Anaphase II, the centromere divides and the then chromatids, now chromosomes, are secreted to the opposite poles of the cell.
- Telophase II
Telophase II is identical to Telophase of mitosis. Cytokinesis separates the cells.
Comparison of Mitosis and Meiosis
:
- Mitosis maintains the level of ploidy while meiosis reduces it.
- Meiosis can be considered as a phase of chromosome number reduction followed by a slightly different mitosis.
- Meiosis only occurs in relatively few cells of a multicellular organism, while mitosis is more common.
