title: Hybrid dysgenesis in Drosophila melanogaster: evidence from sterility and southern hybridization tests that P cytotype is not maintained in the absence of chromosomal P factors.
abstract: A two-generation crossing program was used to replace the entire chromosome complement of P strains by M strain chromosomes, the maternal contribution being from the P strain. The cytotype of chromosomally substituted females was indistinguishable from M strain cytotype, judged by the sterility of offspring from the cross of such females to P strain males. In addition, following replacement of the chromosomes, the level of DNA homologous to the P factor was sufficiently low to be explicable by low levels of P factor transposition. These results are consistent with immediate chromosomal control for the switching from P to M cytotype. However, the reverse chromosome substitution, replacing all chromosomes of an M strain with P chromosomes, did not usually lead to immediate change of cytotype properties, showing that there is a true maternal effect in the M to P direction. The absence of true maternal inheritance for P cytotype argues against models of P factor repression which depend on autonomous replication of a nonchromosomal element. The repression could still be explained by nonchromosomal copies of the P factor, provided that these are replenished from chromosomal P factors. A model is put forward in which P cytotype is due to the presence of circular P factors carrying a P factor target sequence, leading to preferential transposition of chromosomal P factors to nonchromosomal target sites.
mesh_terms: D000818:Animals; D003593:Cytoplasm / Q000502:physiology; D004251:DNA Transposable Elements; D004331:Drosophila melanogaster / Q000235:genetics*; D005260:Female; D006824:Hybridization, Genetic; D007246:Infertility; D008297:Male; D009693:Nucleic Acid Hybridization
chemical_list: D004251:DNA Transposable Elements