 Paradoxically, the rejection of speculations about the nature and functioning of hereditary units advocated by Johannsen opened the possibility for its investigation as an epistemic object. By separating genes and characters more clearly and treating them as correlated in terms of differences rather than in terms of growth or production implied in “Anlage” and similar earlier concepts, characters could take on the epistemic function of an “index” or “marker” informative of the genetic composition of gametes and zygotes (Meunier 2016b; Schwartz 2000). The gene began to take shape as a material entity when this inferential strategy was combined with observations from microscopic studies of reproductive cells that enabled inferences on the role of chromosomes in heredity.