meioosis

Meiosis, sometimes referred to as meioosis, is a specialized form of cell division that reduces the chromosome number by half, producing four genetically distinct haploid cells from a single diploid precursor. It is essential for sexual reproduction in most eukaryotes and contributes to genetic diversity among offspring.

Meiosis consists of two consecutive divisions: meiosis I and meiosis II. In preparation, chromosomes are replicated during the S phase. In meiosis I, homologous chromosomes pair and undergo synapsis to form tetrads; crossing over between non-sister chromatids creates genetic recombinants. The homologous chromosomes then separate, reducing the chromosome number from diploid to haploid. In meiosis II, the sister chromatids separate, similar to a mitotic division, producing four haploid cells.

Genetic variation arises from several mechanisms: crossing over during prophase I, the independent assortment of homologous chromosomes at metaphase I, and the random nature of fertilization. These processes generate offspring with new genetic combinations, increasing diversity in populations.

Meiosis produces different outcomes in different organisms. In animals, it yields gametes (sperm and eggs) that participate in fertilization. In many plants, meiosis gives rise to spores that grow into haploid gametophytes, continuing the life cycle. Errors during meiosis, such as nondisjunction, can lead to aneuploidy, where chromosomes are present in abnormal numbers and may cause developmental disorders.

Meiosis is tightly regulated by cell cycle checkpoints and meiotic-specific controls to ensure proper chromosome pairing, recombination, and segregation.