The production of offspring by sexual reproduction includes the fusion of two gametes, each with a complete haploid set of chromosomes. Gametes are formed from specialised diploid cells.
This specialised kind of cell division that reduces the chromosome number by half results in the production of haploid daughter cells. This kind of division is called meiosis. Meiosis ensures the production of haploid phase in the life cycle of sexually reproducing organisms whereas fertilisation restores the diploid phase.
We come across meiosis during gametogenesis in plants and animals. This leads to the formation of haploid gametes.
The key features of meiosis are as follows:
- Meiosis involves two sequential cycles of nuclear and cell division called meiosis I and meiosis II but only a single cycle of DNA replication.
- Meiosis I is initiated after the parental chromosomes have replicated to produce identical sister chromatids at the S phase.
- Meiosis involves pairing of homologous chromosomes and recombination between them.
- Four haploid cells are formed at the end of meiosis II.
Meiotic events can be grouped under the following phases:
|Meiosis I||Meiosis II|
|Prophase I||Prophase II|
|Metaphase I||Metaphase II|
|Anaphase I||Anaphase II|
|Telophase I||Telophase II|