Chiasma redistribution in presence of supernumerary chromosome segments in grasshoppers: Dependence on the size of the extra segment

Abstract

The presence of two different supernumerary chromosome segments in each of four bivalents of the grasshopper Chorthippus binotatus permitted us to test confidently the effects of such extra material on chiasma distribution in bivalents carrying them, since the same bivalent could carry any of two extra segments differing in nature, size, chromosomal location and C-banding response. All extra segments analysed modified significantly the chiasma distribution pattern, so that chiasmata formed preferentially in the furthest chromosomal regions from the extra segment. The significant difference in the intensity of this effect observed for the two extra segments on the M5 bivalent, however, is presumably due to their very different size, which demonstrates a direct dependence of the intensity of the chiasma redistribution on the size of the extra segment. © 1987, The Genetical Society of Great Britain.