animals tested for effects on alcohol self-administration, one-quarter exhibited increased drinking, one-third exhibited decreased drinking, and 40 percent did not differ from control animals (Crabbe et al. 2006). This finding clearly demonstrates the multiplicity of genetic influences on alcohol responses. As gene-targeting technologies allow more specific experimental regulation of genes than simple deactivation or over-expression, these approaches will continue to provide important data. For example, researchers now can manipulate genes so that they are expressed only in certain cell types or during particular developmental periods.
