Mammalian IgH switch regions. Genomic configuration around Sα (top panel) and Sμ (bottom panel) is as illustrated. Orange ovals represent switch regions, and green rectangles represent constant regions. Restriction enzyme (EcoRI) sites are shown on top. Solid red, blue, green, and purple bars are the locations of qPCR amplicons in the DNA regions containing Sα, upstream of Sα, downstream of Sα and Sμ, respectively.