- Meiosis is a specialised form of cell division that reduces the chromosome number by half, producing haploid gametes essential for sexual reproduction. It occurs in germ cells and ensures that offspring inherit a balanced set of chromosomes from each parent.
- Meiosis consists of two successive divisions, meiosis I and meiosis II, following a single round of DNA replication.
- The hallmark of meiosis is the pairing and recombination of homologous chromosomes, processes that generate genetic diversity and ensure accurate segregation. Proteins such as SYCP3, SYCP1, TEX11, and cohesins play central roles in organising meiotic chromosomes and stabilising recombination intermediates.
- During meiotic prophase I, homologous chromosomes undergo pairing, synapsis, and crossover formation. The synaptonemal complex, a protein scaffold composed of SYCP1, SYCP2, and SYCP3, facilitates the alignment of homologues and supports recombination.
- Crossovers ensure that homologous chromosomes remain physically connected until anaphase I, allowing them to segregate accurately. Meiosis I separates homologous chromosomes, while meiosis II resembles mitosis and separates sister chromatids. Errors in these steps can lead to nondisjunction, aneuploidy, or infertility.
- Meiosis is essential for fertility in both sexes. In males, it occurs continuously during spermatogenesis, producing millions of spermatozoa throughout adult life. In females, meiosis begins during embryonic development, pauses for years, and resumes during ovulation. Disruption of meiotic proteins such as TEX11, SYCP3, or DMC1 can lead to meiotic arrest, reduced gamete quality, or infertility. Conditions such as azoospermia, oligozoospermia, and oocyte maturation defects are frequently associated with meiotic abnormalities.
- Beyond reproduction, meiosis provides insight into chromosome biology, genome stability, and evolutionary genetics. The mechanisms of recombination and chromosome pairing are highly conserved across eukaryotes, from yeast to mammals. Comparative studies reveal that meiotic proteins maintain similar roles across species, highlighting their evolutionary importance. Misexpression of meiotic proteins in somatic cells has been observed in certain cancers, where they may contribute to genomic instability.
Further reading:
- Zickler D, & Kleckner N., 2023. Meiosis: Dances Between Homologs. Annu Rev Genet. 57, 1-63. DOI: 10.1146/annurev-genet-061323-044915, PMID: 37788458, Annualreviews (Download PDF)
- Jones G., et al., 2014. Meiosis through three centuries. Chromosoma. 133(2), 93-115. DOI: 10.1093/jxb/erab217, PMID-34009331, PMCID: PMC8483783 (Download PDF), academic.oup (Download PDF)
