Each GeneChip® was scanned using an Affymetrix Model 3000 scanner and underwent image analysis using Affymetrix GCOS software. Microarray data are available at the National Center for Biotechnology Information's Gene Expression Omnibus, http://www.ncbi.nlm.nih.gov/geo/, under series accession no. GSE13524 [GSM341183…GSM341211] (Barrett et al., 2005; Edgar et al., 2002). Raw .cel files were then imported into the statistical programming environment R (R: A language and environment for statistical computing Ver 2.2.0; R Foundation for Statistical Computing, 2005) for further analysis with tools available from the Bioconductor Project (Gentleman et al., 2004), with these further expanded by the authors using the R language. Expression data from the 27 arrays of the ACB region were normalized and converted to log(2) using the Robust Multi-chip Average (RMA) method (Irizarry et al., 2003) implemented in the Bioconductor package RMA. As a standardization step to facilitate later comparisons with other experiments, expression levels were scaled such that the mean expression of all arrays was log2(1000). Because the primary objective was identifying genes that could be subjected to further bioinformatic analysis, all probesets currently annotated by Affymetrix as
