Cytogenetics of Lolium perenne : Part 1: Chiasma frequency variation in inbred lines.

A number of inbred lines of Lolium perenne have been developed as far as the fifth inbred generation and are being used for basic studies on the cytogenetics of the species. An analysis on variation in the pattern of chiasma frequency and distribution, including the parent plants and all generations down to the S5, reveals that the effect of inbreeding is to reduce chiasma frequency and to increase both the cell and bivalent variances. Evidence is presented for a genetic basis of polygenic control of chiasma formation and distribution, and a model is suggested for control over the three related components of variation which involves a two-stage level of regulation.