Figure 1.

An illustration of the properties required to infer the causal relationship L → T_i → T_j. (a) All gene expression traits are normalized to follow a N(0,1) distribution. By the causality equivalence theorem, in order to conclude that L → T_i → T_j, it must be the case that (b) T_i is linked to L, where the mean expression among segregants with allele at L inherited from the BY parental strain is different from the mean expression among segregants with allele at L inherited from the RM parental strain; (c) T_j is also linked to L; and (d) the expression of T_j given T_i is no longer linked to L. Trigger is an algorithm to estimate the probability that all three conditions (shown in panels b to d) hold simultaneously.