Meiosis is the unique process by which haploid (n) germ cells are produced by two successive cell divisions without an intervening round of DNA replication. This is one of two key events in the alternation of the haploid and diploid phases of the human life cycle, the other being the fusion of the haploid egg and sperm (fertilization) to produce a diploid (2n) zygote.
Two key features of the first meiotic division are the close pairing of homologous chromosomes and their segregation at opposite poles of the meiotic spindle. The first meiotic division, MI, is called the reduction division because it reduces the number of chromosomes from 2n to n. Sister chromatids separate from each other only at the second meiotic, or fusion, division, Mil. This produces haploid cells that differentiate into eggs in females and sperm in males.
Down syndrome, Homologous chromosome, Meiotic division, Chiasm frequency, Germline Stem cell
Meiosis is the process in which the parent cell divides twice into four daughter cells that contain half the original amount of genetic information, i.e. the daughter cells are haploid. Gametes are produced by meiosis. Features of meiosis are discussed below.
Characteristics of meiosis
- It results in the formation of four daughter cells in each cycle of cell division.
- The daughter cells are identical to the parent cell in shape and size but differ in the number of chromosomes.
- The daughter cells are haploid.
- Recombination and segregation take place in meiosis.
- The process occurs in the reproductive organs and results in the formation of gametes.
- The process is divided into two types: meiosis-I reduces the number of chromosomes by half and is known as reductional division. Meiosis-II is like the mitotic division.
- Meiosis is responsible for the formation of sex cells or gametes that are responsible for sexual reproduction.
- It activates the genetic information for the development of sexual cells and deactivates the sporophytic information.
- It keeps the number of chromosomes constant by reducing them by half. This is important because the number of chromosomes doubles after fertilization.
- In this process an independent distribution of maternal and paternal chromosomes takes place. Thus, the chromosomes and the traits controlled by them are rearranged.
- A genetic mutation occurs due to irregularities in cell division by meiosis. Mutations that are beneficial are brought about by natural selection.
- Crossing produces a new combination of traits and variations.