Location of Shfr, a new gene that rescues hybrid female viability in crosses between Drosophila simulans females and D-melanogaster males

As a rule, progeny of crosses between Drosophila simulans females and D. me lanogaster males are formed by sterile males, because females die as embryo s. However, populations of these species have been found that produce a cer tain frequency of viable hybrid females. We have found that 94% of the fema les of a D. simulans population from Tel Aviv gave hybrid progenies with bo th sexes. The segregation of phenotypes with different rescue success adjus ts to the action of a single, dominant, zygotic-acting gene involved in hyb rid female viability. This gene, which we named 'Simulans hybrid females re scue' (Shfr), is temperature-sensitive, showing a much smaller effect as te mperature increases. Reciprocal crosses between Tel Aviv and a nonrescue po pulation indicate some influence of cytoplasm or maternal effect in rescue. Using a chromosome substitution analysis we have located Shfr on the secon d chromosome. Using synthetic lines with this chromosome having different s egments from Tel Aviv and from a multimarker strain we have mapped Shfr bet ween black (2 L-43.0) and pearly (2 R-74.0).