The Integration of Supernumerary Chromosomes into the Orthopteran Genome

Abstract

Supernumerary chromosomes are found in all major eukaryote groups and are widespread in several of the better documented ones such as grasses and grasshoppers. But whereas many aneuploid situations are well-studied and understood, supernumerary or B chromosomes have, in general, received little attention. This stemmed largely from their central paradox, for although some large B chromosomes can each be equivalent to 6% of the diploid genome, they did not appear to have obvious phenotypic effects. In addition, they are generally heterochromatic in appearance, vary in number, and do not pair with regular chromosomes, and, consequently, they have been relegated to the position of a miscellaneous rag-bag. However, recent work has shown that they can have quantitative effects on chiasma formation, chromosome pairing, nuclear histone content, development rate, morphology, and fertility. Another feature of some systems, which also suggests an adaptive role, is their distinct geographic distributions. Using the current information...