Sex-ratio segregation distortion associated with reproductive isolation inDrosophila

Sex-ratio distortion is the most common form of non-Mendelian segregation o bserved in natural populations. It may occur even more frequently than dire ct observations suggest, because the dysgenic population consequences of a biased sex ratio are expected to result in the rapid evolution of suppresso rs, resulting in suppressed or "cryptic" segregation distortion. Here we re port evidence for cryptic sex-ratio distortion that was discovered by intro gressing segments of the genome of Drosophila mauritiana into the genome of Drosophila simulans. The autosomal suppressor of sex-ratio distortion, whi ch is also associated with a reduction in hybrid male fertility, has been g enetically localized to a region smaller than 80-kb pairs in chromosome 3.