Genome elimination mediated by gene expression from a selfish chromosome

Numerous plants and animals harbor selfish B chromosomes that “drive,” or transmit themselves at higher-than-Mendelian frequencies, despite long-term fitness costs to the organism. Currently it is unknown how B chromosome drive is mediated, and whether B-gene expression plays a role. We used modern sequencing technologies to analyze the fine-scale sequence composition and expression of Paternal Sex Ratio (PSR), a B chromosome in the jewel wasp Nasonia vitripennis. PSR causes female-to-male conversion by destroying the sperm’s hereditary material in young embryos in order to drive. Using RNA interference, we show that testis-specific expression of a PSR-linked gene, named haploidizer, facilitates this genome elimination-and-sex conversion effect. Haploidizer shares homology with a gene in Candidatus cardinium, a bacterial symbiont that also induces genome elimination in its insect host.