Accession codes: The raw sequencing data has been submitted to the NCBI Sequence Read Archive under accession number SRA009489. Variant calls for both data sets are available via a mirror site of the UCSC genome browser (ucscbrowser.genenetwork.org). Additionally, 4.875 million SNPs and 0.67 million indels have been submitted to the dbSNP database (www.ncbi.nlm.nih.gov/SNP) using the submitter handle UTHSCSEQ.