The effects of disruptive and stabilizing selection on body size in Drosophila melanogaster. III. Genetic analysis of two lines with different reactions to disruptive selection with mating of opposite extremes

摘要

A genetic analysis was made of two lines which when subjected to disruptive selection with compulsary mating of opposite extremes (D−) showed a different response viz. one, D−-1, showing predominantly an increase of environmental variance and possibly interaction variance, the other, D−-2, showing an increase of genetic variance. Crosses between extreme flies within lines revealed that D−-1 genomes from large flies are dominant to genomes from small individuals. In D−-2 the genetic variation is predominantly additive variance. Tests for dominant chromosome effect in crosses with an inbred stock with recessive markers showed clear third chromosome differences in D−-2 and not in D−-1. Chromosome exchange between extreme flies corroborated the importance of genetic differences in D−-2. A factor or complex of factors with large effect decreasing body size is located on third chromosomes from small flies in D−-2. Interaction between chromosomes has a similar magnitude in the two lines. Crowding and temperature experiments did not reveal an increased general sensitivity to environmental factors in D−-1, which was suggested by the enlarged environmental variance of this line.