Cytogenetic studies on natural populations of grasshoppers with special reference to B-chromosomes

Abstract

In Atractomorpha bedeli the frequencies of males with B-chromosomes in the males from the Tofuro-ato population were 21, 30, 32, 40, and 26%, respectively, over five years. Numbers of B's (0 to 7) in the primary spermatocytes were usually constant within the follicles but were variable among the follicles within the individuals. In males from the Okazyo-ato population, 35% contained B's in their primary spermatocytes. The cells of the gastric caeca were observed in 8 males with B's in the primary spermatocytes but no cells of the gastric caeca contained B's. Cells of ovariole walls and those of gastric caeca were analysed in 80 females from the same population; none of them contained B's. These facts indicate that B's are present in the germ line but absent in the somatic line. The difference between the germ line and the somatic one was explained on the basis of elimination of B's from the somatic cells. The inter-follicular variation in number of B's was ascribed to mitotic non-disjunction in the germ line prior to differentiation of the follicles.