Selection for increased abdominal bristle number in Drosophila melanogaster with concurrent irradiation

Summary Replicate lines, each initially with one hundred pairs of parents selected at 50% intensity, were derived from the Canberra strain. In later generations population size was reduced and selection intensity increased. Three lines were selected without irradiation and five with 1000 r X-rays per generation for thirty generations. Selection was continued until generation 66. Long-term responses were similar in unirradiated and irradiated lines, and there was evidence that genes with large effects influenced response patterns in both groups of lines.This work was carried out while B.H. was on leave from the New South Wales Department of Agriculture, and held a Commonwealth Research Studentship. Robin Hall and Tricia Brown provided much appreciated technical assistance, and we are indebted to the Radio-Therapy Unit, Royal Prince Alfred Hospital, for the use of their equipment.