Variation at metaphase-I inLathyrus

Abstract

Diploid Lathyrus amphicarpos, L. sativus and L. tingitanus (Leguminosae) showed no significant difference in mean chiasma frequency, despite their differences in genome size. Highly significant phenotypic differences were detected within each species. C, autotetraploid L. tingitanus had a chiasma frequency less than double that of the diploid of lowest chiasma frequency but the variance did not significantly differ from four times the pooled within plant variance of the diploids. The supplementary DNA responsible for genomic evolution has no effect on variation in chiasma frequency, either between species or within nuclei. Small but very highly significant differences in chiasma position were observed between the three diploid species examined. In L. amphicarpos, which has the smallest genome of the three (10.0 pg/2C), early chiasmata are distal whereas later chiasmata tend to be interstitial. The converse is true of L. tingitanus, the species with the largest genome (19.2 pg/2C). L. sativus, with the intermediately sized genome (16.2 pg/2C), exhibits an intermediate pattern of chiasma distribution, chiasmata being equally likely to be distal or interstitial whether formed early or late. Each tetrasome in C, autotetraploid L. tingitanus is equally likely to form a quadrivalent. The frequency of ring quadrivalents was nearly twice that of chains. Rings are twice as likely to be in non-disjunctional configurations as chains but both rings and chains are equally likely to be in alternate or adjacent orientation.