MEIOTIC VARIATION IN AN INTERGENOMIC AUTOPOLYPLOID SERIES .1. CHIASMAFREQUENCY

Variation in chiasma frequency has been studied in PMCs of diploids an d C-0 autotetraploids of seven Lathyrus species exhibiting a range of genome size (10.8-19.9 pg DNA/2C). Variation in chiasma frequency show ed no relation to changes in genome size, either between species or be tween disomic sets within nuclei. Mean chiasma frequency of the tetrap loids showed a 75% increase over that in the diploids. Half of this in crease represents an additive effect of chromosome doubling. Total var iance in chiasma frequency of autotetraploids increases by 80% over th at in diploids, in line with the square of the multiplicative effect o f chromosome doubling. At the diploid level, interspecific differences account for the major component of variance (63.1%). Phenotypic varia tion in chiasma frequency was apparent in all seven species but repres ented the smallest component of variance (2.8%). Chromosome doubling r esults in an eightfold increase in the absolute size of the phenotypic component of variance in chiasma frequency and a threefold increase i n that of the cellular component. It has no effect on the absolute siz e of the interspecific component.