(pl. chiasmata) A point at which * chromatids from different homologues in a bivalent are seen to be in close contact as separation of the paired chromosomes commences during the first meiotic * prophase. Genetic evidence shows that at these points the chromatids break and rejoin so portions are exchanged, resulting in the recombination of maternal and paternal genes on the * homologous chromosomes. Chiasma formation is also important for the distribution of chromosomes into the nuclei of gametes. If chiasmata fail to form, homologues do not pair effectively at first prophase and they are unable to move to the poles of the spindle. See also crossing over. |
