Meiotic Behaviour and Dosage Effect of B-Chromosomes on Recombination inDichroplus Elongatus(Orthoptera: Acrididae)

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Abstract
In a previous study (Vilardi 1983, 1985) a polymorphism for a mitotically and meiotically unstable B chromosome was detected in a population of Dicbroplus elongatus from Tucumán (República Argentina). In the present work a detailed analysis of four B carrying individuals from the same population is reported. The B's within an individual were generally telocentric, their number varying from 0 to 6. In some cells, B's were metacentric or acrocentric because of spontaneous rearrangements. At diplotene and diakinesis they could form univalents or pair, in general terminally, rendering bivalents or paseudomultivalents. At first metaphase only univalents or terminally associated B bivalents were observed. These bivalents could persist even to first anaphase migrating undivided to the same pole. Interstitial chiasma frequency and the ratio interstitial/total chiasmata per cell showed an apparent increase as the number of B's per cell were incremented, without significant changes in the total number of chiasmata per cell. The regressions of interstitial chiasma frequency and interstitial/total chiasmata per cell on the number of B's per cell were highly significant (p <0.01). These results would indicate that the B's may influence genetic recombination without changing the total chiasma frequency. The fact of conferring a higher degree of variability in the offspring of B carrying individuals might be one of the causes for the maintenance of these B's in the population.