B6 mRNA sequences for each gene were downloaded from the May 2004 (mm5) UCSC (NCBI Build 33) genome assembly [28]. These sequences were imported along with all CAST sequence traces into the SeqMan sequence assembly program (DNASTAR) and manually curated for quality. Poor quality reads were resequenced. Individual contigs were created for each gene and polymorphisms were detected and curated by manual inspection.