Hybrid Dysgenesis in Drosophila Melanogaster: A Possible Explanation in Terms of Spatial Organization of Chromosomes

Abstract

Male recombination of female sterility, 2 aspects of hybrid dysgenesis in D. melanogaster, were studied in crosses between a locally collected wild population and laboratory strains. Dysgenesis occurs in the F1 hybrid of such crosses only if the wild type is used as male parent and the laboratory strain as female, suggesting an interaction between genotype and cytoplasm. Further crosses are difficult to interpret in terms of a conventional genotype-cytoplasm model, and for dysgenesis to occur it is necessary that the wild-type chromosomes be contributed by the male parent. Receipt of any of the 3 major wild-type chromosomes in crosses to laboratory females is sufficient to cause hybrid dysgenesis. A model of chromosome spatial organization is described. Normal nuclear functioning requires a definite spatial organization of chromosomes, which is presumalby achieved by chromosome-membrane associations. Chromosomes are inherited from the female parent with spatial ordering preserved, i.e., membranes and associated chromosomes are handed on directly from the female parent. Spatial ordering is not necessarily preserved in male gametes, and paternally derived chromosomes carry information enabling them to become correctly organized within the zygote nucleus. Bybrid, dysgenesis results when the chromosome(s) from the male of 1 strain lack the information to become correctly organized in the nucleus of a 2nd strain. The model seems to explain the results, and offers the possibility that the present system may yield information on the genetics of membrane development and other aspects of spatial organization in the normal nucleus.