Preliminary Genetic Analysis of Crossveinless-like Strains of Drosophila Melanogaster.

0 answer the new questions being raised about polygenes and polygenic systems, for example, on the nature of the interactions between specific loci or on the presence of a specific allele in independent selections, requires a special methodology of polygenic analysis. The heart of this methodology is the ability to make controlled substitutions of one gene for its allele in several defined combinations with other genes of the polygenic system. Much of the technical problem and its solution have been outlined by THODAY ( 1961). One part of the solution is to make the preliminary genetic analysis. that is, the localization of the polygenic system to chromosome, by chromosomal isolation methods that lead to isogenic chromosome stock. The point here is that the stocks of isolated, isogenic chromosomes produced for the preliminary genetic analysis are the very materials needed for synthesis of any desired combination of those isogenic chromosomes. The synthetic combinations serve the methodology in the two following ways. First, considered as single-chromosome substitutions in several, defined combinations with other chromosomes, they approximate the goal of controlled, singlegene substitutions in polygenic systems. The information from the chromosome substitutions can give valuable direction to the next, more laborious phase that seeks to identify the loci of the individual genes. Second, used to define the background genotype in linkage analysis, they confine the variation to the regions bounded by the marker loci. In this way the identification of the individual gene locus will not be confounded by irrelevant chance variation. This kind of preliminary genetic analysis is illustrated here. An effective means of gathering polygenes for study is the selection of crossveinless phenotypes in Drosophila. TIMOF~EFF-RESSOVSKY ( 1931,1934) used this selection on D. funebris; PREVOSTI ( 195 1, 1952) used it on D. subobscura; and in the last decade several people, including WADDINGTON ( 1953), BATEMAN (1959), MILKMAN ( 1960a, 1960b, 1964), used it on D. melanogaster. The genetic analyses in this paper are of still other crossveinless-like (cvl) lines, previously reported only in abstracts (MOHLER 1958, 1962).