Osztod

Osztod, in the sense of cell division, is the process by which a parent cell divides to produce daughter cells. In eukaryotes, division occurs mainly through mitosis followed by cytokinesis, yielding two genetically identical diploid cells, or through meiosis, yielding four haploid gametes with genetic diversity. Prokaryotes divide by binary fission, a simpler process not involving a nucleus.

Mitosis is divided into prophase, prometaphase, metaphase, anaphase, and telophase, accompanied by the condensation of chromosomes, assembly of the mitotic spindle, and segregation of sister chromatids to opposite poles. Cytokinesis follows mitosis and completes cell division: in animal cells, a contractile actin ring forms a cleavage furrow that pinches the cytoplasm apart, whereas in plant cells vesicles coalesce to form a separating cell plate.

Meiosis consists of two successive divisions, meiosis I and meiosis II, each with prophase, metaphase, anaphase, and telophase. Meiosis I includes homologous recombination and independent assortment, reducing the chromosome number from diploid to haploid and generating genetic variation among gametes.

Regulation of the cell cycle involves cyclin-dependent kinases (CDKs) and cyclins, with checkpoints that monitor DNA integrity and spindle attachment at the G1/S and G2/M transitions, as well as during metaphase. Errors in division can lead to aneuploidy or genomic instability, contributing to disease, while controlled division supports growth, development, and tissue renewal.

Historical notes indicate that the understanding of mitosis and cell division developed in the late 19th and early 20th centuries, with foundational work by researchers such as Walther Flemming. Rates of division vary by organism, tissue type, and developmental stage, and some cells enter a quiescent state (G0) rather than actively dividing.