THE EFFECTS OF INBREEDING ON BODY WEIGHT AND ABDOMINAL CHAETA NUMBER IN DROSOPHILA MELANOGASTER

Abstract

Twenty randomly chosen lines of D. melanogaster were inbred by full sib mating for 20 generations. Four non-inbred cultures served as controls. Expressed as a deviation from controls, mean chaeta number and body weight did not change, but individual line means tended to fluctuate and disperse. Average within line variance of chaeta number did not change while for weight it did not decrease as much as expected. Residual within line genetic variance due to heterozygosity is suggested. Twelve generations of selection for high and low chaeta number within 3 lines was ineffective; this supports the Tantaway-Reeve hypothesis that natural selection against homozygosity at some loci reduces the rate of fixation and the genotype becomes more sensitive to the effects of further fixation with increasing homozygosity. E is suggested that remaining unfixed loci influencing chaeta number assume increasing importance with respect to fitness with increasing homozygosity. Crosses among the lines suggest that the 3 lines tended to remain heterozygous for many of the same loci.