Parallel Polymorphisms for Interstitial C-Bands and B-Chromosomes inZoniopoda Tarsata(Orthoptera: Romaleidae)

Abstract

SUMMARYThe meiotic behaviour was analyzed in a population from Argentina of Zoniopoda tarsata. By C-banding, interstitial regions of constitutive heterochromatin were evidenced in the three largest (1, 2 and 3) autosomal pairs and the X. The bands of pairs 1 and 3 and a proximal supernumerary heterochromatic block on pair 11 proved to be in polymorphic condition. Besides these polymorphisms, three spontaneous mutants respectively for the absence of the band in one member of pair 2, the presence of a B-chromosome with a procentric C-band, and the presence of two B's with a subterminal band were found. Karyomorphic frequencies for the polymorphisms involving pairs 1 and 3 did not agree with those expected for a Hardy- Weinberg's equilibrium mainly because of deficiency of heterozygotes. This bias was considered consequence of migration from populations composed mainly by homozygotes. Chiasma frequency scores and morphometric measurements were made searching for any effect of the observed polymorphisms. Intrachromosomal effects were observed for pairs 1 and 11 with heterozygotes showing higher frequency of terminal and lower frequency of interstitial chasmata than homozygotes. Heterozygous condition of pair 1 presented also interchromosomal effect reducing the number of interstitial and increasing the proportion of terminal chiasmata. The absence of bands in this pair would cause e reduction of between cell variance of overall chiasma frequency. No effect on chiasma conditions was detected for the heterochromatin polymorphism involving pair 3. Morphometric measurements indicated no effect of any rearrangement on the exophenotype.