Genetic Analysis of Male-Specific Lethality between \u3cem\u3eCaenorhabditis briggsae\u3c/em\u3e:: \u3cem\u3eCaenorhabditis nigoni\u3c/em\u3e F1 Hybrids

Speciation occurs when there is a lack of reproduction due to genetic barriers. These genetic barriers to gene flow are referred as reproductive isolation mechanisms. Pre-zygotic and post-zygotic isolation are types of reproductive isolation mechanisms. In this project, post-zygotic isolation mechanisms were examined. Haldane\u27s Rule states that in F1 hybrids, individuals of the heterogametic sex are less fit than those of the homogametic sex. Darwin\u27s Corollary to Haldane\u27s rule states that there is asymmetry in hybrid progeny between interspecific reciprocal crosses. Crosses done between Caenorhabditis briggsae males to Caenorhabditis nigoni females produce viable F1 hybrid females and males, yet the F1 hybrid males are infertile. When compared to reciprocal crosses, the F1 hybrid females are viable, but males die during embryogenesis. When cbr-him-8(v188) was used to study male-specific lethality, it was found that cbr-him-8 acts as a recessive maternal-effect suppressor of F1 hybrid male-specific lethality. A possible mechanism for suppression is epigenetic meiotic silencing due to unpaired X chromosomes. F1 hybrid males with an X chromosome from C. briggsae when crossed to various females generated progeny. Other F1 hybrids males that acquired X chromosome from C. nigoni paternally, were infertile. This demonstrates that hybrid sterile gene must be on the X chromosome of C. nigoni. Thus, X-autosome interactions are essential in determining the incompatibilities of asymmetrical crosses that result in hybrid lethality and sterility