Meiosis
- There are two processes by which the nucleus of a eukaryotic cell can divide. These are:
- Mitosis
- Meiosis
- Mitosis gives rise to genetically identical cells and is the type of cell division used for growth, repair of damaged tissues, replacement of cells and asexual reproduction
- Meiosis gives rise to cells that are genetically different from each other and is the type of cell division used to produce gametes (sex cells)
- During meiosis, the nucleus of the original 'parent' cell undergoes two rounds of division. These are:
- Meiosis I
- Meiosis II
Meiosis I
- The nucleus of the original 'parent' cell is diploid (2n) i.e. it contains two sets of chromosomes
- Before meiosis I, these chromosomes replicate
- During meiosis I, the homologous pairs of chromosomes are split up, to produce two haploid (n) nuclei
- At this point, each chromosome still consists of two chromatids
- Note that the chromosome number halves (from 2n to n) in the first division of meiosis (meiosis I), not the second division (meiosis II)
Meiosis II
- During meiosis II, the chromatids that make up each chromosome separate to produce four haploid (n) nuclei
- At this point, each chromosome now consists of a single chromatid
One diploid nucleus divides by meiosis to produce four haploid nuclei