CHROMOSOME-BANDING PATTERNS IN LETTUCE SPECIES (LACTUCA SECT LACTUCA,COMPOSITAE)

Chromosome banding patterns obtained with C- and N- banding, and AgNO3 staining were studied in somatic metaphase complements of four Lactuc a species. L. sativa and L. serriola have almost identical chromosome morphology, and L. saligna differs only slightly from them, but L. vir osa is quite distinct from the other species. A gross comparison of th e banded karyotypes suggests a closer relationship of L. saligna to L. sativa/serriola than to L. virosa. Our data agree with the results of previous crossing experiments in these species but conflict partly wi th recent RFLP data which indicate a closer phenetic relationship of L . saligna to L. virosa than to L. sativa/serriola. Such a discrepancy may be explained assuming that domestication of L. sativa/serriola res ulted in an increased selection pressure on unique DNA sequences as de monstrated by the RFLP data. Differential evolution of specific hetero chromatin classes (and presumably of highly repetitive DNA classes), a s revealed by chromosome banding techniques was not linked to domestic ation. Thus the disparity in conclusions about relationship (in terms of genetic similarity) as based on the different experimental approach es reflects a non-parallel evolution of highly repetitive vs. unique D NA classes.