Extrachromosomal element delta in Drosophila melanogaster: VI. Induction of recurrent lethal mutations in definite regions of second chromosomes

Abstract

The extrachromosomal element denoted by delta in Drosophila melanogaster was found to induce frequent recessive lethal mutations on the second chromosome. The average mutation rate of lethals induced was 1.47% in the presence of delta b, being about 3–4 times the spontaneous mutation rate (0.41%). A number of instances of mutation clustering were observed. Hence, delta b appears to induce the mutation at the premeiotic cell stage. A total of 113 lethal genes originating independently were found to locate at 27 different sites on the chromosome. The locations of these sites were determined and it was found that the distribution of lethals along the chromosome was markedly nonrandom; lethals were strongly concentrated upon units 0–10 (13.3%), 55–65 (30.1%) and 70–85 (50.4%) of the genetic map, and there was a notable absence of lethals in the 35 map-units immediately to the left of the contromere.