Unstable alleles of the singed locus in Drosophila melanogaster with reference to a transposon marked with a visible mutation

Summary The gene clw can be integrated into another site in the X chromosome to form the mutable two gene transposon system sn::Tn-clw. When brought under the common control of the transposon, sn and clw can concomitantly mutate and manifest themselves. Tn-clw was found to move from the sn region to a position of±52 m.u. This transposition was associated with changes in sn::Tn-clw:(1) loss of the instability property by the sn ⁺ allele; (2) appearance of a new lethal allele, clw ⁹, designated as a transposon allele. Based on analysis of the direction and frequency of the sn-clw mutations, the unstable genes of the sn locus were grouped in three pleiades. Interallelic mutations occurred regularly at frequencies of 0.1%–5.6% with changes in the manifestation of the clw mutation specific to each pleiade. Transition from one pleiade to another was rare (5×10^–4), and it was associated with a new phenotypic expression of the sn and clw alleles. The mutational differences between the pleiades are presumably related to differences in the localization of Tn-clw within the sn locus.It was shown that the presence of Tn promotes recombination events in the rightmost portions of the sn-oc interval.