Imprinting and paternal genome elimination in insects.

Abstract

In many insects and other arthropods, males transmit only maternally inherited chromosomes (White 1973; Brown and Chandra 1977; Nur 1980, 1990a,b,c; Bell 1982; Bull 1983; Lyon and Rastan 1984; Lyon 1993; Wrensch and Ebbert 1993; Brun et al. 1995; Borsa and Kjellberg 1996). This remarkable genetic asymmetry can result from any of three principal systems of paternal genome exclusion, each of which has evolved several times. The most familiar and widespread exclusion system is arrhenotoky, in which fatherless males develop from unfertilized eggs and therefore lack paternal chromosomes at all stages of development. Most arrhenotokous systems are genetically haplodiploid, but a few are based on other modes of inheritance (see Nur 1980, 1990c; Bell 1982; Suomalainen et al. 1987). In the two other kinds of exclusion systems, a male’s paternally inherited chromosomes are actively eliminated: males begin life as seemingly conventional diploid zygotes but then either (1) lose their paternal chromosomes during embryonic development, becoming true maternal haploids (embryonic elimination), or (2) exhibit dramatically non-Mendelian patterns of meiosis and spermiogenesis, such that mature sperm carry only maternal chromosomes (germline elimination). To denote their formal (transmission-genetic) similarity to haplodiploid arrhenotoky, the embryonic and germline elimination systems are often characterized as parahaplodiploid or pseudoarrhenotokous.