Meiotic behaviour of the holocentric chromosomes of Nezara viridula (Insecta, Heteroptera) analysed by C-banding and silver impregnation

Abstract

While silver impregnation reveals the presence of kinetochores in monocentric chromosomes, it does not do so in the holocentric system of Nezara viridula. Here, C-banding and silver impregnation techniques reveal that C-heterochromatin is present in the greater part of the Y chromosome and at the nucleolus organizer region (NOR) of the largest autosome (A 1) and in the extra NOR located in the X chromosome of a single exceptional male. Furthermore, one telomere of each autosome appeared lightly C-banded. The largest, A1, bivalent shows chiasmata almost always located at the chromosome ends. This bivalent may orient axially or equatorially in metaphase I cells depending on whether it carries a single chiasma or two chiasmata, respectively. From our cytological analysis we deduce that centromeric activity is preferentially located at the two telomeric ends and that the presence of chiasmata at an end excludes such activity.Key words: diffuse centromere, C-banding, holocentric, insect chromosomes.