The genetics of a new mutable allele at the white locus in Drosophila melanogaster

Summary The genetics of a third case of high mutation frequency at the white locus in Drosophila melanogaster has been analyzed. The new mutable allele, w ^+u, mutates from a wild-type to a white-eyed phenotype in both males and females. The mutational event is 1) premeiotic, 2) not associated with crossingover, 3) sensitive to genetic modification, and 4) restricted to germinal tissue. The only mutants produced by w ^+u are deletions of the white locus. These deficiencies include subsites 4 and 5 of the white locus, but are cytologically unobservable. The mutable allele itself maps to subsite 4.The mutational properties of w ^+u are unlike those of the other highly mutable white alleles which have been interpreted in terms of phage-like controlling elements. Rather, the properties of w ^+u favor a model based on the premature termination of chromosome replication near the terminus of a replicon which leads to a chromosome deficient for the material between the point of premature termination and the end of the replicon.Supported by NIH predoctoral traineeship GM-150 and by NIH research grant GM-07428 to Dr. W. K. Baker.From a dissertation submitted to the Division of Biological Sciences of The University of Chicago in partial fulfillment of the requirements for the degree of Doctor of Philosophy.