Hybrid Dysgenesis in DROSOPHILA MELANOGASTER: Sterility Resulting from Gonadal Dysgenesis in the P-M System.

Crosses between two types of strains, called P and M, characteristically give high frequencies of F(1) sterility and other aberrant traits. Previous studies indicated that, in addition to the direction of the parental cross, many factors influence the manifestation of this phenomenon known as "hybrid dysgenesis."-The present study is concerned with the characteristics of GD (gonadal dysgenesis) sterility associated with the P-M system and its temperature dependence. Female sterility is accompanied by a complete absence of egg-laying, and this is not attributable to an inability to mate. Thus, it seems likely that sterility results from a defect in gametogenesis of hybrid individuals. This conclusion is supported by the morphological and cytological observations presented in an accompanying paper (Schaefer, Kidwell and Fausto-Sterling 1979).-A narrow, critical, developmental temperature range was found in which both female and male sterility rose sharply from a low level to a high maximum. The critical range was 27 to 29 degrees for males, slightly higher than the range of 24 to 26 degrees for females. Two other dysgenic traits, male recombination and transmission ratio distortion, were affected by developmental temperature, but temperature response curves were quite different from those for sterility. The temperature-sensitive stage for female sterility occurs during embryonic and early larval development.-GD sterility is compared and contrasted with SF sterility, another specific type of non-Mendelian sterility resulting from a different interstrain dysgenic interaction.