Chiasma frequency and distribution in a sample of human males: chromosomes 1, 2, and 9.

Chiasma frequency and the distribution of chiasmata within chromosomes 1, 2, and 9 were investigated in a total of seven males with presumptively normal meiosis. With the exception of one unusual individual there was little variation among the males examined for these characteristics. The exceptional male had a reduced chiasma frequency, which, rather than being considered abnormal, was thought to represent the lower end of the normal range of variability. A statistical analysis of the histograms of chiasma distribution confirmed the impression of overall similarity, and we conclude that genetic maps of these chromosomes may now be constructed without too much disturbance from differences between individuals. The maps will be presented separately in a subsequent paper.