Meiosis, unlike mitosis, creates daughter cells that have half as many chromosomes as the parent cell (Figure 1).
Meiosis is preceded by an interphase consisting of the G1, S, and G2 phases, which are nearly identical to the preceding phases mitosis. During DNA duplication in the S phase, each chromosome is replicated to produce two identical copies, called sister chromatids, that are held together at the centromere by cohesin proteins. Cohesin holds the chromatids together until anaphase II.
Figure 1 Meiosis proceeds in two steps. During meiosis
The function of meiosis:
Reduce the number of chromosomes from diploid to haploid
Ensure each daughter cells has a complete set of chromosomes
Generate genetic diversity among the daughter cells
Meiosis consists of two nuclear divisions, meiosis I and meiosis II, that reduce the number of chromosomes to the haploid number, in preparation for sexual reproduction. In meiosis
Synapsis and crossing over. During prophase
I 1, the homolog pairs up and is held by synapsis. Crossing over also happens during prophase I 1.
Homologous pairs at the metaphase plate. During metaphase
I 1, homologous chromosomes come together to pair along their entire length. This pairing doesn’t occur in mitosis.
Separation of homolog. During anaphase
I 1, the homologous chromosome pairs separate, but the individual chromosome, each consisting of two sister chromatids remain intact.
In meiosis II, the sister chromatids are separated.