Further evidence for the theory that crossover interference in Drosophila melanogaster is dependent on genetic rather than physical distance between adjacent crossover points

Effect of heat shock on certain meiotic parameters in Drosophila melanogaster was studied in the cv-v-f region of the X chromosome of females homozygous for mus309 mutation, deficient in DNA double-strand break repair, or being of wild type. The heat shock in the wild females caused that the frequencies of the single crossovers and all the map lengths decreased while the frequency of the double crossovers and crossover interference remained unchanged. In the mus309 mutants all parameters remained unchanged except that single crossovers in the cv-v interval were less frequent, and that crossover interference diminished. Thus, heat shock seems have two separate effects; one being independent on the mus309 gene and affecting the occurrence of crossing over itself, and the other being dependent on the mus309 gene and affecting some precondition of crossing over. This precondition is probably the choice between two routes of the repair of double-strand DNA breaks known to be controlled by the mus309 gene. The results are in accordance with the genetic models of interference in which interference depends on genetic distance between the crossover points, but in contradiction with physical models where interference is dependent on physical distance between the crossover points.