Fig. 1

Definition of direct and indirect genetic effects and experimental design. a Direct genetic effects (DGE, blue) on an individual’s phenotype arise from the individual’s own genotypes; indirect genetic effects (IGE, red) arise from genotypes of interacting partners (cage mates). This panel illustrates a situation where all individuals are genetically heterogeneous and both DGE and IGE arise from each individual’s genotypes. b IGE on a phenotype of interest arise when two individuals interact and (unknown) heritable traits of one individual, the social partner, influence the phenotype of interest measured in the other individual, the focal individual. For a given phenotype of interest, the correlation ρ between DGE and IGE is equivalent to the correlation between DGE on the phenotype of interest and DGE on the traits mediating IGE on the phenotype of interest. Importantly, this correlation can be estimated even when the traits mediating IGE are not known or not measured. c Experimental design. A list of the 170 phenotypes collected on each mouse is presented in Additional file 3: Table S2