a peak location in the middle. Because linkage is a within-family test, whereas association is a between-family test, it is also possible that genetic heterogeneity between families could contribute to a detectable linkage signal for which association tests would not be able to detect the underlying genetic variants. This is another possible explanation for the failure to identify any genes directly under the linkage peak. Systematic follow-up across the entirety of chromosome 2 also yields significant evidence of association with multiple other genes that appear to map loosely to the more distal linkage peaks that have been reported on the p and q arms of the chromosome. A preponderance of genes involved in alcohol dependence and related traits across the chromosome likely contributes to the consistent implication of this chromosome in linkage scans.
