Hybrid dysgenesis in Drosophila melanogaster: rules of inheritance of female sterility

摘要

Hybrid dysgenesis has been described as a syndrome of aberrant traits including sterility, male recombination, and mutation, which occurs in some inter-strain hybrids of Drosophila, but only from one of the two reciprocal crosses. In a series of experiments in which hybrids of various pedigrees were tested for sterility, it was found that a case of hybrid dysgenesis could be most easily interpreted as the interaction of two components. One component was found to be a polygenic Mendelian factor linkedto each of the major chromosomes of phi_2, the paternally contributing strain ('P strain'). These chromosomes were capable of causing sterility when inherited from either parent, provided the appropriate maternal component was also inherited. The ability to transmit this maternal component was designated ' cytotype' to indicate that it is a property of the entire cell. It was possible to classify nearly all hybrid females as either P or M cytotype on the basis of their ability to produce sterile daughters. All daughters of the M -cytotype mothers were susceptible to the sterilizing effects of the phi_2 chromosome, whereas all, or nearly all daughters of P-cytotype mothers were immune. When more than one of the phi_2 chromosomes were received by daughters of M-cytotype females, chromosomal interactions could be detected statistically, but the model of independent action remained a useful approximation. Cytotype was shown to be determined by chromosomal factors, but with Hmited cytoplasmic transmission. This unusual mode of inheritance can be compared with other cases of hybrid dysgenesis where the behaviour resembles that of self-replicating cytoplasmic particles which are dependent on certain chromosomes. The lack of sterility from intra-strain crosses can be explained by the fact that chromosomes capable of causing sterility also induce the P cytotype, and thus prevent sterility in the next generation.