Abstract

The chiasma distribution of bivalents 15 and 16 identified at diakinesis by a quadruple staining technique including DA-DAPI fluorescence has been investigated in two human males. The study has shown that chiasmata are not distributed at random. Both chromosomes have distally localised chiasmata, but in the long arm of chromosome 15 chiasmata are also found to be localised proximally, adjacent to the centromere. Genetic lengths and recombination fractions have been calculated from chiasma distribution data for the major bands of chromosomes 15 and 16 under the assumptions that there is no chromatid interference, no chiasma movement, and no difference between mitotic and meiotic band positions. The localisation of chiasmata implies much discrepancy in recombination patterns between the acrocentric chromosome 15 and the submetacentric chromosome 16.