Physical mapping of the single linked marker, D6Mit13, and the two closest unlinked markers, D6Mit61and D6Mit374, was performed in silico based on the May, 2004 build of the public B6 genome. Based on these marker positions, the size of the QHCl chromosome 6 QTL is less than 5.0 Mb (Figure 3). This region contains a number of known genes, all but eleven of which encode members of two large receptor families: natural killer cell lectin-like receptors, and T2R-type taste receptors. The Tas2r genes (which encode the T2Rs) are found clustered within a 1.2 Mb interval on either side of D6Mit13 (Figure 3, Figure 4). Because of their proximity to the linked marker, their demonstrated expression in taste receptor cells, and their role in the detection of at least some bitter-tasting compounds, we hypothesized that one or more of the 24 Tas2rs at this locus were responsible for the major QHCl taste sensitivity QTL.