An examination of the role of chiasma frequency in the genetic system of marsupials.

Chiasma frequencies have been collected from males of 33 species of marsupial, varying widely with respect to size, reproduction and development. Correlation analyses show that species with lower levels of recombination are smaller, have larger litters and develop more quickly. Two indices of recombination level were considered: Darlington's Recombination Index, and the Excess Chiasma frequency (chiasmata above one per bivalent). The EC is in general more strongly correlated than RI with aspects of life history. It is suggested that EC levels have evolved due to the effects of EC on recombination, but that chromosome number has evolved independently.