The three types of chiasma formation in acrocentric chromosomes. The drawing illustrates the crossover patterns/chiasma formation and reciprocal recombination between homologous chromatids in acrocentric chromosomes, which as regards singles and doubles are basically the same in mice and humans. Note that the different chromatids from the two homologs are randomly selected, i.e. there is no chromatid interference. A single chiasma is most often positioned either medially or more distal towards the telomere (top). Two chiasmata are located more near to the centrome and telomere (middle). Three chiasmata are located, respectively, adjacent the centromere, medially and adjacent to the telomere. Reproduced from .