EFFECT OF GENETIC BACKGROUND ON MUTATION FREQUENCY OF INSERTIONAL ALLELES OF THE LOZENGE GENE IN DROSOPHILA-MELANOGASTER

We studied the effect of genetic background on mutation frequency of a n unstable lz(75V) allele of the lozenge gene (lz; 1-27.7) isolated fr om natural populations of Drosophila melanogaster and its mutant deriv atives lz(B) and lz(sl). Genetic composition of the X chromosome conta ining unstable alleles (X(75V) chromosome) was shown to affect their m utability. The region of the chromosome proximal to lozenge contains f actors required for high mutability of lz(75V) and lz(B). Susbtitution Of a distal part of the X chromosome from a laboratory strain for a h omologous part of the X(75V) chromosome also resulted in stabilizing l z(75V), but caused an increase in mutation frequency of lz(B). Associa tion between instability of lz(75V) and the presence of P element with in the locus was revealed by in situ hybridization. Studying effects o f regulatory elements from a pi(2) P strain showed that the P cytotype is associated with a twofold to threefold decrease in mutation freque ncy of lz(B) and lz(sl), but P-M hybrid dysgenesis is associated with its slight increase. Regulation of instability of the lozenge gene wit hin the X(75V) chromosome was assumed to involve three levels: (1) cha racter and topography of a mobile element inserted into the locus, (2) regulatory factors of other X-chromosomal regions, and (3) cytoplasmi c factors. The results obtained are discussed in terms of regulation o f transposition of mobile genetic elements.