A group of four cells formed by meiosis. All four cells may survive to form spores, as occurs in the formation of pollen grains. Alternatively some of the cells abort, as in the angiosperm ovule, where one cell develops into the embryo sac and the remainder abort. The four cells of the tetrad may remain joined together. This provides a useful system for the study of the nature and extent of recombination, a procedure termed tetrad analysis. The shape of the tetrad, e.g. whether it is linear, tetrahedral, tetragonal, or rhomboidal can be a useful taxonomic character and is a major factor determining pollen morphology. See also triradiate scar. |
