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. 2008 Mar 31;105(13):5277–5281. doi: 10.1073/pnas.0710225105

Fig. 2.

Fig. 2.

Infant distress vocalization as a function of the OPRM1 C77G genotype (C/C, ■, or C/G, ▴). Values are mean frequencies of vocalizations (± SEM) during the chronic phase of four consecutive (S1–S4) cycles of mother–infant separation. 77G carriers showed overall higher vocalization [main effect of genotype: n = 25 vs. 64; F(1,88) = 5.2, P = 0.025], and had a differential temporal course of the response over successive separations [genotype × time interaction, F(3,246) = 4.2, P = 0.007]. The OPRM1 C77G genotype and its interaction with separation exposure accounted for 9.4% of the observed variance in vocalization.