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Recent advances in behavioral genetics suggest a modest relationship among certain gene variants, early childhood experiences, and criminal behavior. Although scientific research examining this link is still at an early stage, genetic data are already being introduced in criminal trials. However, the extent to which such evidence is likely to affect jurors’ decisions has not been explored. In the present study, a representative sample of the U.S. population (n = 250) received a vignette describing an apparently impulsive homicide, accompanied by one of four explanations of the defendant’s impulsivity: childhood abuse, genetic predisposition, childhood abuse and genetic predisposition, or simple impulsive behavior. The participants were asked to identify the crime that the defendant had committed and to select an appropriate sentence range. Evidence of genetic predisposition did not affect the crime of which the defendant was convicted or the sentence. However, participants who received the abuse or genetic + abuse explanation imposed longer prison sentences. Paradoxically, the genetic and genetic + abuse conditions engendered the greatest fear of the defendant. These findings should allay concerns that genetic evidence in criminal adjudications will be overly persuasive to jurors, but should raise questions about the impact of genetic attributions on perceptions of dangerousness.