The relationship between synapsis and chiasma distribution in grasshopper bivalents heterozygous for supernumerary segments

Abstract

The relationship between chiasma distributions and pairing behaviour of grasshopper bivalent heterozygous for supernumerary segments has been analysed. The extra segments were located at the telomeric end of the long arm in chromosome S8 of Chorthippus jacobsi and at interstitial position in chromosomes S8 and M7 of Euchorthippus pulvinatus. In all cases these heteromorphic bivalents exhibited fully paired synaptonemal complexes with equalized axial lengths either at late zygotene or early pachytene, that is, heterosynapsis in regions near the extra segments is achieved at these meiotic stages. It is proposed that the absence of chiasmata in those regions in which nonhomologous pairing took place, would lead to chiasma redistributions observed in these bivalents when compared with those observed in bivalents in which extra segments are lacking. © The Genetical Society of Great Britain.