The Arabidopsis genome is relatively small, completely sequenced and well annotated.  High-density oligonucleotide arrays designed from that sequence measure gene transcript abundance as well as sequence polymorphisms.  A single assay can genotype over one million loci making it possible to routinely map induced mutations to within 1 Mb using BSA (bulk segregant analysis) or directly delineate large deletions.  Extending this approach to a panel of 100 recombinant inbred lines (RIL), array-genotyping defined 815 recombination breakpoints.  This unprecedented level of genetic linkage mapping accuracy and resolution (0.6 cM) makes for fine QTL mapping.  Each RIL was also transcription profiled and thousands of loci controlling quantitative difference in expression levels (eQTLs) were mapped.