A chiasma map of man.

By fitting compounds beta distributions to chiasma frequencies the physical map obtained from banded chromosomes has been converted into a chiasma map giving the distribution of observed chiasmata in relation to several hundred cytological bands, assuming proportionality of mitotic and meiotic chromosomes. This is a genetic map if there is a precise correspondence between sites of chiasmata and crossing-over. However, if there is appreciable preanaphase movement of chasmata, then the chiasma map is a serious distortion of the genetic map. Predictions from the chiasma map can be confirmed or refuted only by genetic evidence for which the estimates of this paper serve as initial values to begin maximum likelihood iteration.