Wadington’s genetic assimilation experiment, in 1953, was one of the first experiments that claimed the inheritance of an acquired character. In this experiment, he applied a heat shock to flies triggering a low frequency of a “crossveinless” (cve) phenocopy (posterior crossvein defects in the adult wing). Through repeated selection of this trait with heat-shock, he was able to fix cve in the population. Waddington also believed that if the classic experiment were to be repeated with a different foundation stock, the same phenotypic effect might be produced. Microarray analysis comparing RNA expression in the wing imaginal discs of heat-shocked pupae between two laboratory fly stocks (wild-type canton S flies and w1118 strain) identified novel genes that were differentially expressing in the w1118 strain. Thus showing that both strains differ considerably in their capacities for cve production Resequencing the whole genome suggests that cve alleles are common, naturally occurring polygenes spread on all three major chromosomes of Drosophila, and that they act additively to produce wings with disturbed posterior crossveins. Widespread position effects in the genome alter key epigenetic and developmental processes to produce the phenocopy.
Author(s): Ajay Nair, Peter K Dearden