[Effect of the transposon at the singed locus on recombination in Drosophila melanogaster]

Recombination frequency in different combinations of unstable alleles of the sn49::Tn-clw system was studied. In some diallele combinations, an increased recombination frequency in the region of signed gene was found. The distribution of mutant progeny in the compounds was different in recombination and non-recombinant classes. Restriction mapping of the Tn-clw transposon revealed that it contained conservative and variable sequences. Interallelic transitions were associated with rearrangement of the variable sequence and the signed sequences adjacent to the transposon.

[A derivative of the X(Z) chromosome causes a change in the mutability properties of genes in homologous chromosomes from unstable lines of Drosophila melanogaster]

The impact of an XZ chromosome derivative, the In(1)T2,ymosWYIsnmYI strain, on mutation and reversion frequencies in strains with the unstable yellow gene is analyzed. These strains were isolated during a yellow mutation outbreak observed in the natural population of Drosophila melanogaster in Uman' (Ukraine) from 1982 to 1991. The In(1)T2,YmosWYIsnmYI chromosome was shown to suppress yellow gene mutability and activate singed gene mutability. A possible mechanism of homologous suppression and destabilization is considered.

[The unstable system sn(49) in Drosophila melanogaster: results of blot-hybridization and polymerase chain reaction]

A set of 40 strains of alleles of different phenotype and mutation frequency, derived from unstable system sn49 of Drosophila melanogaster, was obtained. A mutation in the singed gene or the formation of a visible de novo mutation in the studied X chromosome served as the criterion for strain isolation. Total DNA was isolated from the obtained strains and used for blot-hybridization and polymerase chain reaction (PCR). Rearrangements were found within the first intron of the singed gene. In the first intron of an allelic derivative of this unstable system, an inserted sequence of at least 4 kb in length was found. Using PCR primers from this intron, fragment length polymorphism in different derivatives was revealed.

[Emergence of a recessive lethal mutation in derivatives of an unstable X(Z)-chromosome from Drosophila melanogaster]

Xz chromosome isolated from a natural population of Drosophila melanogaster is characterized by spontaneous mutability of the genes yellow, white, and signed and the appearance of chromosomal rearrangements. In mutant lines derived from the line carrying the Xz chromosome that had one, two, or three unstable visible mutations (markers), the rate of appearance of sex-linked lethal mutations was analyzed. This rate was shown to increase with an increase in the number of markers in a line. This phenomenon, termed "marker induction", might explain the phenotypic homogeneity of natural Drosophila populations. Spontaneous lethal mutations were mapped, and their nonrandom distribution along the Xz chromosome was shown. Along with common "hot spot" of lethal mutations, the derivatives for the Xz chromosomes had their own specific sites for lethal mutations. In some cases, the appearance of lethal mutations was accompanied by the formation of inversions in the Xz chromosome. The lethal destabilization of the Xz derivatives, caused by selection for accumulation of visible mutations, is associated with an increase in the number of hot spots for lethal mutations. Presumably, these hot spots are hot sites for the transposition of mobile genetic elements.

[A mutable X(Z)-chromosome isolated from a natural population of Drosophila melanogaster]

In 1986, a mutable XZ-chromosome, in which mutation at genes yellow, white, and singed were recorded, was isolated from a natural population of Drosophila melanogaster from Zaporozh'e. Visible mutations in the region garnet-forked were also detected. Mutations appeared at a rate of about 10(-4) and were probably postmeiotic. Cytological analysis showed that two types of inversions occurred independently in XZ-chromosome. Specific features of this chromosome are hypermutability of the white locus (the mutation rate was approximately 10(-3) and a hot spot for chromosomal rearrangements in the terminal segment of the X-chromosome.