Genetic analysis of the Hybrid male rescue locus of Drosophila

Several hybrid rescue mutations-alleles that restore the viability of norma lly lethal hybrids-have been discovered in Drosophila melanogaster and its relatives. Here we analyze one of these genes, Hybrid male rescue (Hmr), as king two questions about its role in hybrid inviability. (1) Does the wild- type allele from D. melanogaster (Hmr(mel)) cause hybrid embryonic inviabil ity? (2) Does Hmr(mel) cause hybrid larval inviability Our results show tha t the wild-type product of Hmris neither necessary nor sufficient for hybri d embryonic inviability. Hmr(mel) does, however, appear to lower the viabil ity of hybrid larvae. The data further suggest (though do not prove) that H mr(mel) acts as a gain-of-function poison in hybrids. These findings suppor t previous claims that hybrid embryonic and larval lethalities are genetica lly distinct and suggest that Hmr(mel) is at least one of the proximate cau ses of hybrid larval inviability.