MUTATION BURSTS AT THE YELLOW LOCUS IN A NATURAL-POPULATION OF DROSOPHILA-MELANOGASTER ARE ASSOCIATED WITH A HOBO INSERTION

In 1981, a recurrent local burst of high mutability and high allele fr equency of the yellow gene was recorded in the natural population of D rosophila melanogaster from Uman', Ukraine. A detailed genetic analysi s showed that hypomorphic alleles y(2) prevailed during the mutation b urst. Mutations were strictly allele-specific and occurred only in two directions: from y(2) to y(+) and from y(+) to y(2). Alleles y(2) iso lated from the natural population differed in the degree of instabilit y of mutant and wild-type derivatives, expression of the mutant phenot ype, and complementation properties. In this work, the insertion natur e of all unstable alleles derived from the natural population is confi rmed by direct molecular methods. The mutation burst at the yellow loc us is shown to result from insertion of a defective hobo copy. Six mut ations y(2) independently isolated from the natural population were ca used by an insertion of hobo in the same site of the yellow regulatory region. The hobo copies were identical according to the restriction m ap. In three y(2) alleles, the mutant phenotype was associated with in version between hobo copies, one of which was located in the yellow lo cus and the other, in another unidentified region of the X chromosome, The remaining y(2) alleles were associated with deletions that were l ocated in the vicinity of the hobo insertion site and in the region of yellow enhancers.