What is Meiosis? – Definition
Meiosis is a kind of cell division in which cell is permanently transformed into a gamete and cannot divide again until fertilization.
The term meiosis was coined by J.B. Farmer and Moore.
It is required to continue reproductive cycle of eukaryotes. Meiosis results in gametes with one half of the numbers of chromosomes of the parent cell.
Kinds of meiosis
Kinds of meiosis on the basis of time at which it takes place
| Type | Occurrence time | Examples |
|---|---|---|
| Terminal or gametic meiosis | Before formation of gametes | few lower plants |
| Intermediary or sporic meiosis | At some intermediate time between fertilization and the formation of gametes. | Flowering plants |
| Initial or zygotic meiosis | Immediately after fertilization | Algae, fungi |
Meiocytes are the cells in which meiosis takes place. Meiocytes of plant sporangium are called as sporocytes i.e. micro and mega sporocytes.
Meiosis is the two step, one-way process, it cannot be said to engage in a cell cycle as mitosis. (See Difference between Mitosis and Meiosis)
The complete procedure of meiosis is given as Meiosis – Stages – Process
- Division I (Heterotypic division)
- Division II (Homotypic division)
Significance of Meiosis
- Maintains a definite and constant number of chromosomes i.e. ploidy level in organisms.
- Genetic diversity allows a species to maintain stability under environmental changes, variation is necessary for natural selection.
- Crossing over during prophase I and independent assortment at both of the meiotic divisions during meiosis promote variation. Independent assortment of chromosomes allows genetic variation among gametes. Results in new genetic combinations within chromosomes.