Supernumerary chromosome segments and intrabivalent chiasma redistribution in Pyrgomorpha conica (Orthoptera)

Abstract

Two kinds of supernumerary chromosome segments have been found on the megameric chromosome of the grasshopper Pyrgomorpha cónica. One of them is euchromatic and distally located while the other one is heterochromatic and proximally located. Their effects on chiasma distribution in heterozygous, homozygous and doubly heterozygous bivalents for these segments have been analyzed. Both segments distort chiasma distribution so that the single chiasma is preferentially formed far from the location of each supernumerary segment. This effect is more pronounced in bivalents that are homozygous for the presence of the proximal heterochromatic segment. In doubly heterozygous bivalents that possess both segments on the same chromosome the chiasma distribution is significantly different from that observed in heterozygous bivalents for each segment and a significant frequency of univalents was scored. © The Genetical Society of Great Britain.