On the Mechanism of Heterosis-The Chromosomal or Cytoplasmic Basis for Heterosis in Drosophila melanogaster

Abstract

This paper presents a study of vigor in random bred stock and inbred and homozygous races of Drosophila melanogaster. Egg production is used as a measure of vigor. The results show that inbreds from continued brother by sister pair matings may retain some of their genes in heterozygous condition over many generations. "Homozygous" lines, formed by outcrossing, in general, show lower yields than the inbreds from which they originated. This observation would agree with the hypothesis that the cause of hybrid vigor lies in differences in genic interaction between alleles and their reaction products. This result would not be expected if the cause of hybrid vigor lay in some, as yet unidentified, physiological stimulation resulting from the union of unlike gametes.