Genetics of inbred Drosophila melanogaster. XXIII. Diversity in cytoplasmic elements affecting recombination.

From an inbred line of Drosophila melanogaster, in which both marker genes in the X-chromosome and an autosomal inversion had been induced, we introduced the genome into cytoplasms of various sources. Two or eight sister-lines were established from three sets of cytoplasms. Tests of recombination in the distal y--rb region in isogenic females revealed similarity in early broods within sets of sister-lines, but differences between different sources of cytoplasms. Later broods showed increasing recombination and also greater variability. There was a clear excess of recombination in offspring to inversion-heterozygous females. In the set with eight sister-lines there were two groups of four, which during the first 4.5 years had been propagated with 14 and 28 days generation interval respectively. These two groups differed in the inter-chromosomal effect in early broods. The possibility is discussed that there are more than one set of extra-chromosomal elements that affect recombination in the distal region of the X-chromosome. It is concluded that selective forces operate on the extra-chromosomal elements in other ways than in the process with which they were traced in the tests. The consequences of diversities in extra-chromosomal elements are discussed.