ABSTRACT
Due to the complete absence of ribosomal DNA (genetic symbol bb-), the Xbb- chromosome of Drosophila is lethal both in homozygous conditions and in compound with the Xbb- chromosome. However, in the cross between the C(1)RM/Ybb- females and the Xbb-/BSYbb+ males, characterized by the development of lethal Xbb-/Ybb- zygotes, two fertile males were detected. These males possessed all the markers of the Xbb- chromosome but lacked the Y chromosome BS marker. Genetic analysis of their progeny showed that genes responsible for restoration of viability and fertility of these exceptional males were associated with the X chromosome. The crossover tests showed that in one case these genes were tightly linked to the w locus (the bbAM1 allele), and in the second case they were located 12.6 map units to the right of the Tu locus (the bbAM7 allele). It has also been shown that the bb locus was transposed to the X chromosome within the short arm of Y chromosome. Transposition of the BSYbb+ chromosome-specific rDNA sequences to the X chromosome was confirmed by means of Southern blotting. These data indicate that replacement of the bb locus is realized by transposition rather than recombination.
Subject(s)
DNA Transposable Elements , Drosophila melanogaster/genetics , Animals , Blotting, Southern , Crossing Over, Genetic , DNA, Ribosomal , Drosophila melanogaster/enzymology , Female , Homozygote , Male , X Chromosome , Y ChromosomeABSTRACT
Molecular analysis of several mutations of the white locus was performed. The mutations were obtained as a result of mutagenesis in the unstable white-starka locus described previously. A large insert (approximately 15 kb in length) downstream of the first exon of the white gene was shown to be partly excised. Simultaneous excisions of various regions from the natural regulatory region of the white locus were also observed. Restriction enzyme analysis showed that the observed mutations and reversions resulted from large deletions from the regulatory gene region. Southern and Northern blot hybridization showed the presence of unknown regulatory regions within and outside the insert.
Subject(s)
ATP-Binding Cassette Transporters , Alleles , Drosophila Proteins , Drosophila/genetics , Eye Proteins , Insect Proteins/genetics , Mutation , Animals , Blotting, Northern , Blotting, Southern , Chromosome Mapping , Regulatory Sequences, Nucleic Acid , Sequence DeletionABSTRACT
In 1992, Bashkirov et al. described the case of occurrence in line C(1)RM, yw/0; Dp(1; 3) wvco/+ of a unique female with light, uniformly colored eyes. This trait was not inherited together with Dp(1; 3) wvco but was linked to the X chromosome. We denoted this new allele as white-starka (wstr). It proved to be unstable, demonstrating mutational transitions to other allelic states with frequencies of 10(-3) to 10(-5). Southern blot analysis showed that the wstr mutation was induced by an insertion of an unknown sequence with a length approximately evaluated by the authors in 1992 as 7 kb. Using a wider spectrum of restriction endonucleases and a prolonged gel running, we were able to estimate the size of this insertion more precisely. According to our data, in the case of wstr we are dealing with an insertion in the locus white of a sequence 15.1 kb long. As seen from our restriction map of the allele wstr, this insertion does not resemble retroposons with long terminal repeats, but is possibly similar to LINE mobile elements of Het-A and TART types, characteristic for heterochromatin.
