Meiosis I is the reductional division that converts a diploid germ cell into two haploid cells, proceeding through prophase I, metaphase I, anaphase I, and telophase I with cytokinesis, and differing from mitosis in one defining respect: in anaphase I the sister chromatids remain joined at their centromeres while the homologous pairs are separated to opposite poles, so that chromosome number is halved rather than conserved. Two mechanisms operating during this division generate genetic variation among the resulting gametes — chromosomal crossover in prophase I, in which homologous segments of homologous chromosomes carrying the same genes but potentially different alleles are exchanged, and the random orientation of each homologous pair at the metaphase plate, which makes the assortment of maternal and paternal chromosomes into daughter cells independent. The mechanical work of alignment and segregation is performed by the spindle: microtubules emanating from centrosomes attach at kinetochores and push the poles apart while moving chromosomes. This concept belongs to cell biology and genetics, specifically the chromosomal basis of sexual reproduction, and it explains why gametes are both haploid and genetically non-identical, the precondition for inherited variation.
Meiosis I is the reductional division that converts a diploid germ cell into two haploid cells, proceeding through prophase I, metaphase I, anaphase I, and telophase I with cytokinesis, and differing…