Gene-Wise Differences in Rat and Mouse Responses to TCDD. A) The specific identity of genes showing TCDD-induced changes in mRNA abundances diverges significantly between rats and mice. Only 33 genes are found altered in both species and, of these, 3 are altered in different directions. Thus only 15% of rat responses (30/200) and 10.8% of mouse responses (30/278) to TCDD are conserved in homologs from the other species. B) To test if genes with strong evidence (low p-values) for differential expression in one species would have similarly strong evidence (low p-values) in the other we plotted the adjusted p-values for the two species in log10 space. Surprisingly these values are strongly anti-correlated (Spearman's rho = -0.60, p < 2.2 × 10-16), suggesting that genes that have strong evidence for differential expression in one species are generally likely to have weak or no evidence in the other.