F1 hybrids from (AKR/J x FVB/NJ) and (DBA/2J x FVB/NJ) outcrosses display a 20-fold difference in mammary tumor metastatic capacity, due to differences in inherited polymorphisms. Expression studies were performed to determine whether polymorphism-driven gene expression signatures predictive of outcome could be generated from normal tissues Keywords: Basal transcription profiles Overall design: Spleen from adult F1 animals from (AKR/J x FVB/NJ) and (DBA/2J x FVB/NJ) outcrosses was collected and arrayed on Affymetrics chip to identify basal differences in gene expression between the different genotypes