Fig. 1.

Infant attachment as a function of the OPRM1 C77G genotype. Attachment was measured as factor scores (mean ± SEM) extracted from a range of behaviors scored during a critical developmental phase (18–24 months of age) as described in Table 1. Scores were significantly higher in 77G allele carriers [n = 27 vs. 69; F(1,94) = 5.6, P = 0.017]. The proportion of variance in attachment behavior accounted for by the OPRM1 C77G genotype, measured as partial eta², was 5.7%.