Cyp1a1, Cyp1a2, and AhR gene expression in the skin and liver of AhR(+/+), AhR(+/−), and AhR(−/−) mice, with and without B[a]P treatment. One-microgram aliquots of RNA extracted from skin and liver of control and B[a]P-treated mice of the three genotypes were reverse-transcribed and analyzed by PCR using specific primers for the Cyp1a1, Cyp1a2, and AhR and β-actin genes.