PARALLEL POLYMORPHISM FOR SUPERNUMERARY SEGMENTS IN CHORTHIPPUS PARALLELUS (ZETTERSTEDT) .3. ASHURST POPULATION

Heterochromatic supernumerary segments, present in either or both the M7 and the S8 chromosomes of the Ashurst (AS) population of Chorthippus parallelus, lead to a significant elevation in mean cell chiasma frequency. This effect appears to be dosage independent within both the S8 and the M7 karyomorphs when these are considered separately. Neither is there any marked interaction between the two systems when they are combined with one another. The selective factors controlling the distribution of S8 karyomorphs within the population appear, however, to act quite independently of those which regulate the M7 karyomorph pattern. This is revealed in two ways. First, whereas the frequency of S8 karyomorphs conform to the expectations of a Hardy-Weinberg distribution those of the M7 do not. Secondly, though the pattern of distribution of S8 types is uniform throughout the AS population that of the M7 is not. This heterogeneity of M7 karyomorphs implies that the population is in some way internally stratified in terms of its breeding structure. © 1969 Springer-Verlag.