Cytological Regulation of Recombination in <i>Pennisetum</i> and <i>Brassica</i>

Abstract

The restriction of recombination through chiasma frequency was investigated in Pennisetum and Brassica where outbreeding is controlled by two different genetic mechanisms. Lines with known inbreeding coefficients were utilised for this purpose. Self-compatible and self-incompatible Brassica material subjected to five generations of disruptive selection for flowering was also included.A consistent increase was observed in the mean chiasma frequency per cell of Pennisetum and Brassica inbreds as compared to the outbred populations. The increase was parallel with the degree of inbreeding in Pennisetum. Disruptive selection for flowering increased chiasma frequency in Brassica populations with the exception of late self-incompatible group.The buffering mechanism of chiasma frequency under inbreeding, referred to as cytological homeostasis, was examined from the viewpoint of the genetic diversity of the populations, the past history of selection, the ecological conditions under which the material is grown, the nature of the breeding system and the fitness-flexibility axis. It is concluded that a compromise between fitness and flexibility is arrived essentially by regulation of recombination through cytological homeostasis and the breeding system.