[Genetic analysis of a polygenic system for a quantitative character after negative and positive selection. II. Chromosome contributions to the expression of the radial vein fragments].

Hybridological genetic analysis of a polygenic system of the character radius incompletus in Drosophila was conducted by intercrossing the contrasting selection lines riSN and riSP and crossing them with the tester line y bw st ri. Two vein segments were shown to have different polygenic systems which control penetrance and expressivity of the character. Determination of the proximal segment was additive with regard to the contribution of the haploid genomes in the hybrid zygote and to the contribution of different chromosomes. The contributions of individual chromosomes of the riSN line compared to those of the tester line were equal to -0.97 (1), -0.31 (2), and -0.14 (3). The contributions of the chromosomes of the riSP line were 0.26 (1), 0.095 (2), and 0.31 (3). Determination of the distal segment was nonadditive in all respects. Specifically, in the hybrid zygotes of riSN and the tester line, the absence of the distal segment was completely dominant over its presence; for that, only one riSN chromosome was necessary. Both intergenomic and interchromosome contributions were nonadditive. The results are discussed with regard to penetrance, expressivity and morphological mechanisms of the longitudinal wing vein formation in Drosophila.