Genetics, Vol 139, 1585-1599, Copyright © 1995

INVESTIGATIONS

Horka, A Dominant Mutation of Drosophila, Induces Nondisjunction and, Through Paternal Effect, Chromosome Loss and Genetic Mosaics

J. Szabad, E. Mathe and J. Puro
Department of Biology, Albert Szent-Gyorgyi Medical University, H-6720 Szeged, Hungary Institute of Genetics, Biological Research Center of the Hungarian Academy of Sciences, H-6726 Szeged, Hungary

Fs(3) Horka (Horka) was described as a dominant female-sterile mutation of Drosophila melanogaster. Genetic and cytological data show that Horka induces mostly equational nondisjunction during spermatogenesis but not chromosome loss and possesses a dominant paternal effect: the X, second, third and the fourth chromosomes, but not the Y, are rendered unstable while undergoing spermatogenesis and may be lost in the descending zygotes. The frequency of Horka-induced chromosome loss is usually 2-4% but varies with the genetic background and can be over 20%. The X chromosome loss occurs during the gonomeric and the initial cleavage divisions. Loss of the X and fourth chromosomes shows no correlation. We propose, based on similarities in the mutant phenotypes with the chromosome destabilizing mutations nonclaret disjunctional and paternal loss, that the normal Horka(+) product is required for function of the centromeres and/or nearby regions. Horka is a convenient tool for the generation of gynandromorphs, autosome mosaics and for the study of gene expression in mosaics.