Cytogeography and the evolutionary significance of B-chromsomes in relation to inverted rearrangements in a grasshopper species.

COLOMBO, P.C. AND CONFALONIERI, V.A.

CYTOGENETICS AND CELL GENETICS

S Karger AG

Lugar: Basilea, Suiza; Año: 2004 vol. -- p. 351 - 358

0301-0171

The analysis of the geographic distribution of polymorphic cytological markers, briefly termed as cytogeography, can be considered as an important tool to be applied when studying the evolutionary significance of chromosome variability within a species, either to unravel the adaptive significance of chromosome polymorphisms or to investigate the parasitic nature of some genomic elements. In this article we review cytogeographical patterns of distribution of inversion and B chromosome polymorphisms. Several lines of evidence that issue from the analysis of the geographic distribution of polymorphic markers suggest that inverted chromosomes are special sequences that are maintained by deterministic forces. On the other hand, the pattern of distribution of B chromosome polymorphism clearly demonstrates its selfish nature, being more frequent in those populations in central environments. We also present the analysis of 272 individuals of T. pallidipennis from Uspallata, and demonstrate that Bs in this population have some influence on body size, enlarging many of the morphometric characters of individuals and we propose it could be the consequence of its genotypic disequilibrium with one inversion. These investigations anre finally discussed with regard to the models proposed for the maintenance of B chromosomes in natural populations and in relation to the possible interactions with chromosome inversions