Meiosissa

Meiosissa is the Finnish term for meiosis, the specialized cell division that reduces the chromosome number by half to form haploid gametes in sexually reproducing organisms. It encompasses two sequential divisions, meiosis I and meiosis II, preceded by a round of DNA replication.

During meiosis I, homologous chromosomes pair and undergo synapsis, forming tetrads. Crossing over occurs between non-sister chromatids, creating new allele combinations. This genetic recombination increases variation among gametes. Homologous chromosomes are then separated to opposite poles in anaphase I, while sister chromatids stay together, resulting in two haploid cells with duplicated chromosomes.

In meiosis II, the two cells divide again. The centromeres split, and the sister chromatids segregate toward opposite poles, producing four haploid gametes with unreplicated chromosomes. Meiosis II resembles mitosis in its mechanics but begins with haploid chromosome sets.

Meiosis generates genetic diversity through crossing over, independent assortment of homologous chromosomes, and random fertilization. Errors such as nondisjunction can produce aneuploidy, including conditions like trisomy or monosomy, and are a major source of developmental disorders.

Meiosissa is essential to sexual reproduction, enabling variation that can fuel adaptation and evolution. Regulation involves cell-cycle checkpoints and meiotic-specific controls that coordinate chromosome pairing, recombination, and division timing.