VARIATION AT METAPHASE-I IN LATHYRUS

Diploid Lathyrus amphicarpos, L. sativus and L. tingitanus (Leguminosa e) showed no significant difference in mean chiasma frequency, despite their differences in genome size. Highly significant phenotypic diffe rences were detected within each species. C-1 autotetraploid L. tingit anus had a chiasma frequency less than double that of the diploid of l owest 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 v ariation in chiasma frequency, either between species or within nuclei . Small but very highly significant differences in chiasma position we re observed between the three diploid species examined. In L. amphicar pos, which has the smallest genome of the three (10.0 pg/2C), early ch iasmata are distal whereas later chiasmata tend to be interstitial. Th e converse is true of L. tingitanus, the species with the largest geno me (19.2 pg/2C). L. sativus, with the intermediately sized genome (16. 2 pg/2C), exhibits an intermediate pattern of chiasma distribution, ch iasmata being equally likely to be distal or interstitial whether form ed early or late. Each tetrasome in C-1 autotetraploid L. tingitanus i s equally likely to form a quadrivalent. The frequency of ring quadriv alents was nearly twice that of chains. Rings are twice as likely to b e in non-disjunctional configurations as chains but both rings and cha ins are equally likely to be in alternate or adjacent orientation.