If one (or more) Tas2rs underlie the chromosome 6 QHCl taste sensitivity QTL, we would predict that one (or more) Tas2r genes would exhibit one of three likely characteristics: (1) A Tas2r allele is a pseudogene, or is deleted, in D2 (QHCL-insensitive), but not B6 (QHCl-sensitive), mice; (2) Missense mutations in the single coding exon of a D2 Tas2r allele impact protein functions such as ligand binding or receptor coupling to downstream signaling cascades; (3) Mutations in noncoding or regulatory regions of a D2 Tas2r allele affects expression of the protein product. Though we considered all three of these to be valid possibilities, we initially focused on the likelihood that deletion or mutation within the coding sequence of a single D2 Tas2r would correlate with the QHCl taste insensitivity phenotype.