Genetics of Natural Populations. Viii. Concealed Variability in the Second and the Fourth Chromosomes of Drosophila Pseudoobscura and Its Bearing on the Problem of Heterosis

Studies on Homeostasis and Heterozygosity I. General Considerations. Abdominal Bristle Number in Second Chromosome Homozygotes of Drosophila melanogaster

“…By now it is well established, for Drosophila at least, that chromosomal homozygotes are with few exceptions lethal, semi-lethal, or sub-vital as compared with heterozygotes. (Dobzhansky, Holz and Spassky, 1942;Dobzhansky and Spassky, 1943;Wallace, 1952;and Wallace and Madden, 1953).…”

Studies on the Interaction of Mutations Affecting the Chaetae of Drosophila Melanogaster. Ii. The Relation of Character Expression to Size in Flies Homozygous for Polychaetoid, Hairy, Hairy Wing, and the Combinations of These Factors

“…While it appears probable that "concealed genetic variability" of the type recently stressed by DOBZHANSKY et al (1942) is the major cause of the phenomena of heterosis, a possible secondary role of factor interactions such as have been described above cannot be disregarded entirely.…”