New hypotheses about the origin of supernumerary chromosome segments in grasshoppers

Abstract

The existence of euchromatic supernumerary chromosome segments which do not seem to represent repeated material cannot be explained by the current hypotheses (duplication or translocation) concerning the origin of extra segments. An hypothesis is proposed to explain the origin of the euchromatic extra segments distally located on the megameric M6 chromosome of the species Omocestus bolivari and Ckorthippus binotatus, namely that these segments represent a relic of an euchromatic region which formed part of the ancestral M6 chromosome of the gomphocerine grasshoppers. On the other hand, the absence of paracentromeric C-bands in some chromosomes of Ckorthippus vagans and Ck. brunneus could have been achieved by means of transformation of heterochromatin into euchromatin. © 1987, The Genetical Society of Great Britain.