Untersuchungen über polygene suppressor-wirkungen auf semiletalfaktoren des X-chromosoms von Drosophila melanogaster

Abstract

Six different X-chromosomes of Drosophila melanogaster carrying a semilethal factor were introduced into an attached-X-strain. Since in such a strain the X-chromosomes of fathers are transmitted to sons this has resulted in a reduced number of male offsprings. After a few generations, however, the viability of the males has increased in almost all cases. Excluding the possibility of backmutations on the semilethal locus the assumption was made that the reduction of semilethality was due to epistatic gene interaction. By backcrossing males of the improved lines to attached-X-females of the original strain the viability of males decreased slightly without reaching the initial values of the experiments. From these and other observations it was assumed that both interaction between genes of the autosomes and interaction between new spontaneous mutant genes and the semilethal genes were active in determining the viability of the males. Intrachromosomal interactions, however, seem to be more important than interchromosomal interactions. The gene action is determined by its genetic background and, with respect to the problem of the genetic load, this has to be taken into consideration.