∞ generated and posted on 2016.02.23 ∞

Nuclear division involved in generating either gametes or spores.

Meiosis is mechanistically similar to mitosis but involves two divisions, the first of which (meiosis I) has the effect of reducing the number chromosomes going from parent to daughter cells by one-half (so-called reduction division). In addition, crossing over as well as genetic recombination more generally occurs during the first of the meiotic divisions.

The second meiotic division, meiosis II, is very mitosis-like, involving the division of already DNA-replicated but nevertheless haploid cells.

These two divisions of meiosis can be further subdivided into steps that also hark back to mitosis. These steps are:

…then meiosis I through cytokinesis:

…then meiosis II through cytokinesis:

In particular, molecular recombination takes place during prophase I. Independent assortment as well as the transition from diploidy to haploidy also take place during anaphase I.

Whereas in animals meiosis results in the formation of cells that mature into the familiar eggs and sperm, in fungi as well as plants and various algae, meiosis can be involved instead in generating spores, which are haploid cells (like gametes) but which give rise to haploid multicellular organisms that then produce gametes via mitosis. The conspicuous part of the mosses (gametophyte generation), for example, are initiated by spores, which then give rise, eventually, to gametes.

The following video provides a cartoon animation of the process of genetic recombination and reduction division in eukaryotes: