Signal-to-background ratios under different hybridization conditions. Labeled mouse liver RNA (Cy5) and Universal Mouse Reference RNA samples (Cy3) were hybridized with MWG mouse 20 K using GlassHyb™ buffer or 5× SSC, 0.1% SDS buffer with different concentrations of formamide: A. GlassHyb™ buffer. B. 27% formamide. C. 35% formamide. D. 40% formamide. Oligo, mouse-specific probe; Control, Arabidopsis-specific probe; Blank, no probe printed.