[Effect of genetic background on mutation frequency of insertional alleles of the lozenge in Drosophila melanogaster].

We studied the effect of genetic background on mutation frequency of an unstable lz75V allele of the lozenge gene (lz; 1-27.7) isolated from natural populations of Drosophila melanogaster and its mutant derivatives lzB abd lzsl. Genetic composition of the X chromosome containing unstable alleles (X75V chromosome) was shown to affect their mutability. The region of the chromosome proximal to lozenge contains factors required for high mutability of lz75V and lzB. Substitution of a distal part of the X chromosome from a laboratory strain for a homologous part of the X75V chromosome also resulted in stabilizing lz75V, but caused an increase in mutation frequency of lzB. Association between instability of lz75V and the presence of P element with the locus was revealed by in situ hybridization. Studying effects of regulatory elements from a pi 2 P strain showed that the P cytotype is associated with a twofold to threefold decrease in mutation frequency of lzB and lzsl, but P-M hybrid dysgenesis is associated with its slight increase. Regulation of instability of the lozenge gene within the X75V chromosome was assumed to involve three levels: (1) character and topography of a mobile element inserted into the locus, (2) regulatory factors of other X-chromosomal regions, and (3) cytoplasmic factors. The results obtained are discussed in terms of regulation of transposition of mobile genetic elements.