Temporal Changes in the Roles of Lethal and Semilethal Chromosomes within Populations of Drosophila melanogaster

Abstract

An analysis of the viabilities of individuals heterozygous for lethal and semilethal chromosomes obtained from experimental populations of D. melanogaster suggests (1) that these chromosomes exhibit very little dominance (if any) on the average when the homologous chromosome is one of the two genetically-marked laboratory chromosomes, CyL or Pm; (2) that, in contrast, these same chromosomes exhibit an average enhancing effect on viability in combination with other wildtype chromosomes from the same population; and (3) that the latter effect has arisen during the existence of the laboratory populations.