chiasma (pl. chiasmata) In genetics, a cross-shaped structure forming the points of contact between non-sister chromatids of homologous chromosomes, first seen in the tetrads of the diplotene stage of meiotic prophase I. Chiasmata are thus the visible expression of crossing-over of genes. There are usually one or more chiasmata per chromosome per meiosis. See also BREAKAGE and REUNION.

chiasma (pl. chiasmata) In genetics, a cross-shaped structure that forms the points of contact between non-sister chromatids of homologous chromosomes first seen in the tetrads of the diplotene stage of meiotic prophase. Chiasmata are thus the visible expression of crossing-over of genes. There are usually one or more chiasmata per chromosome per meiosis. See also BREAKAGE AND REUNION.

chiasma (pl. chiasmata)The point at which paired homologous chromosomes remain in contact as they begin to separate during the first prophase of meiosis, forming a cross shape. A number of chiasmata can usually be identified and at these points crossing over occurs.