ACHIASMATE SEGREGATION OF X-UNIVALENTS AND B-UNIVALENTS IN MALES OF THE GRASSHOPPER EYPREPOCNEMIS-PLORANS IS INDEPENDENT OF PREVIOUS ASSOCIATION

B chromosomes proved to be more frequent in males than females of the grasshopper Eyprepocnemis plorans collected from the population in Jet e (Granada, Spain) in 1992. The meiotic behaviour of the X and B univa lents was analysed in a high number of 1B males collected from this po pulation in 1991 and 1992, and in males from another population (Salob rena, Granada, Spain) for comparison. These two chromosomes showed a s ignificant tendency to migrate to opposite poles in the Jete populatio n, during the 2 years analysed, but separated randomly in the Salobren a population. Thus, sex differences in the B frequency in Jete seemed to be due to the non-random X-B segregation during male meiosis. The a nalysis of association patterns between the two univalents over severa l stages of the first meiotic division indicated a heterochromatic aff inity rather than association by chiasmata because most X-B associatio ns had resolved by metaphase I. The X and B chromosomes share two diff erent DNA sequences, so that some associations during prophase I undou btedly involve homologous DNA sequences. The frequency with which X an d B migrated to opposite poles at anaphase I in Jete, however, did not show any significant dependence on previous association at zygotene, diplotene or metaphase I.