For chromosome 4, prior linkage evidence for the maximum drinks phenotype has been reported [1], making this a chromosome of special interest. Using the Illumina markers for chromosome 4, we then tested for linkage in the first stage using a regression of the estimated IBD status against the squared sum and squared difference of the trait values, as implemented by the program MERLIN-REGRESS [4]. As this analysis method is computationally intensive, we applied it only to chromosome 4, allowing a more comprehensive study of this chromosome of interest.
