ACME SMART PUBLICATION
Meiosis and its significance
Meiosis is a type of cell division that results in the production of four gamete cells and a 50% reduction in the number of chromosomes in the parent cell. To develop egg and sperm cells for sexual reproduction, this process is necessary. There are four haploid daughter cells formed during meiosis (containing half as many chromosomes as the parent cell).Following are the main characteristics of meiosis:
- Meiosis requires just one cycle of DNA replication but two successive cycles of nuclear and cell division called meiosis I and meiosis II.
- After the paternal chromosomes have duplicated to form identical sister chromatids at the S phase, meiosis I begins.
- Meiosis involves the pairing and recombination of homologous chromosomes.
- At the end of meiosis II, four haploid cells are produced.
Events of Meiosis are classified as:
Meiosis 1
Prophase I: When compared to the prophase of mitosis, the prophase of the first meiotic division is often longer and more complex. Based on chromosomal behaviour, it has been further split into the following five phases: Leptotene, Zygotene, Pachytene, Diplotene, and Diakinesis.
Leptotene: The chromosomes begin to condense at this stage and are connected to the nuclear membrane via their telomeres.
Zygotene: A synaptonemal complex forms between homologous chromosomes at the start of synapsis.
Pachytene - During this stage, genetic material is transferred between chromatids that are not sisters. This is called crossing over.
Diplotene - At this stage, homologous pairs are still connected at the chiasmata after synapsis has ended and the synaptonemal complex has vanished.
Diakinesis: Before metaphase 1, the nuclear membrane finally breaks down and the chromosomes are entirely condensed.
Metaphase I: The bivalent chromosomes line up on the equatorial plate during metaphase I. The spindle's opposing poles' microtubules connect to the pair of homologous chromosomes.
Anaphase I: Sister chromatids are still connected at their centromeres during anaphase I, but homologous chromosomes split.
Telophase I: Cytokinesis occurs after the nuclear membrane and nucleolus re-emerge, and this is known as the "diad of cells." Even though the chromosomes do experience some dispersion in many instances, they rarely reach the interphase nucleus's very stretched state. Interkinesis, which occurs between the two meiotic divisions, is typically a transient stage. Prophase II, which is substantially less complex than prophase I, comes after interkinesis.
Meiosis 2:
Prophase II: Following cytokinesis, meiosis II begins right away, typically before the chromosomes have fully expanded. Meiosis II resembles a typical mitosis in contrast to meiosis I. By the end of prophase II, the nuclear membrane is gone. Chromosomes once more become condensed.
Metaphase II: Chromosomes align at the equator during metaphase II, and sister chromatids' kinetochores get attachments of microtubules from the spindle's opposing poles.
AnaphaseII: Beginning with the simultaneous division of each chromosome's centromere (which had been binding the sister chromatids together), anaphase II allows the chromosomes to migrate toward their respective poles of the cell.
Telophase II: Telophase II marks the completion of meiosis, during which the two chromosomal groups are once more encased in a nuclear membrane. Cytokinesis then takes place, culminating in the production of a tetrad of cells, or four haploid daughter cells.
Significance of Meiosis:
Even though the process itself paradoxically reduces the number of chromosomes by half, meiosis is the mechanism that allows sexually reproducing animals to maintain the particular chromosomal number of each species throughout generations. From one generation to the next, it also makes the population of organisms more genetically variable. For the process of evolution, variations are crucial.
