∞ generated and posted on 2016.12.23 ∞
Association of homologous pairs of chromosomes during meiosis I.
|Tetrad refers to the grouping together of four double helices, that is, four sister chromatids in the course of crossing over, synapsis, and just plain lining up on the metaphase plate during meiosis I.|
It is within tetrads that chiasmata form and crossing over occurs. Synapsis, in turn, refers to the process by which themselves tetrads form.
There thus exists a progression of events that roughly goes something like this: synapsis → tetrads → chiasmata → crossing over → molecular recombination → genetic recombination.
Additional genetic recombination then occurs with the subsequent independent assortment, which in fact takes place as tetrads are separated. This separation occurs during anaphase I of meiosis, and is into separate chromosomes consisting of sister chromatid pairs (rather than of individual sister chromatids). Tetrads thus are substantial contributors to the occurrence of genetic recombination during meiosis.
Tetards are called tetrads because they consist of the interaction of sister chromatid pairs, which in turn consist of individual sister chromatids. A tetrad thus consists of four sister chromatids and also of a total of four double helices. "Tetrad" in turn comes from Greek and means "four".
Note that tetrad is used here in a chromosomal sense and is not to be confused with tetrad meaning bacterial cellular arrangements consisting of groups of four cells arranged into the shape of a square.