Proximal chiasmata induce non-disjunctional orientation of robertsonian trivalents in a grasshopper

Abstract

The relationship between the symmetry of the meiotic configuration and the type of meiotic orientation (disjunctional and non-disjunctional) in Robertsonian trivalents of Dichroplus pratensis (Melanoplinae, Acrididae) was analysed. The results indicate, first, that neither chromosomal size nor the relation between the length of the chromosomes involved in each fusion are important factors for the determination of the orientation. Second, chiasmata localization, which in turn determines effective inter-centromeric distance, may be central. A high positive correlation between proximal chiasma frequency and non-disjunctional orientation at Prometaphase I and Metaphase I was found. These results are in agreement with the hypothesis that the shorter the inter-centromeric distance the greater is the probability that both centromeres migrate to the same pole. The importance of these results is also discussed in relation to the stability of the polymorphisms in this species. © The Genetical Society of Great Britain.