In genetics, reaction range (also known as range of reaction) is when the phenotype (expressed characteristics) of an organism depends both on the organism's genetic characteristics (genotype) and the environment.
For instance, two siblings raised together can have radically different IQs and natural talents. Because of genetic variations between the two siblings and how these variations interact with their environment a wide range of personality/achievement possibilities can lead to an almost infinite range of phenotype possibilities for the individual siblings involved. This range of reactions to the combination of genetics and environment is at the crux of the "nature vs. nurture" debate. Reaction range is the spectrum of phenotypic possibilities that either of these siblings could end up with due to the interaction of their specific genes and the environment they are exposed to.