a likely biological model suggests an increased probability that the interaction is a false positive finding. We provide the framework for this evaluation process in Fig. 3. Note that in the situations represented in Fig. 3c to 3f, whether the slope difference (A or B) that has the opposite sign is significant, determines whether the implied genetic model is likely to be sensible. Only when the slope difference with the sign opposite the other two slope differences is nonsignificant does the interaction represent a recessive or dominant genetic model. Otherwise, the interaction reflects overdominance, a situation whereby the mean of the heterozygous group is not between the means of the two homozygous groups. The existence of overdominance is thought to be rare and remains somewhat controversial (Lynch and Walsh (1998)). We propose that, based on the current state of knowledge and the high propensity for post hoc explanations in the G × E literature, interactions that do not correspond to a classic genetic model (additive, dominant, or recessive) should be viewed skeptically without a clear reason why a more complex genetic model is appropriate for that study. We have listed the situations in which one would conclude that a significant
