The cytoplasm and quantitative variation in Drosophila

Abstract

Our knowledge of the role of the cytoplasm in heredity is largely limited to examples in which notable differences have attracted the attention of workers who were not expecting them. Most of these involve cytoplasmic differences that are themselves under nuclear control though a few involve comparatively independent cytoplasmic entities. Even in so intensively studied an organism as Drosophila melanogaster , such examples of cytoplasmic inheritance are rare, and consequently we think of cytoplasmic variation in such organisms as more a matter of differentiation than of heredity. We are probably right but we would, nevertheless, be wise to be cautious. It is in the nature of genetical experiment that it can only study variation, and the greatest advances we have made in studying nuclear effects have been very much dependent on our ability to make differences for subsequent investigation, using X-rays for major genes, selection for polygenes. We have hardly begun the attempt to make cytoplasmic differences for study and until we have tried to do so we may underestimate the cytoplasm’s role in heredity.