Gene expression patterns of DDX5 and GAPDH from 66 Affymetrix microarray chips using three different probe level quantile normalizations. The gene expression patterns of two internal controls, DDX5 (A) and GAPDH (B: 212581_x_at and C: M33197_3_at) from Affymetrix chips by MAS5 (marked by diamonds), RMA (marked by squares) and GC-RMA (marked by triangles) probe level quantile normalizations. Normalization was performed per chip and per gene using GeneSpring® 7.3 software. The expression levels of these two internal controls were related to the median of the intensities on the 66 chips. The DDX5 expression patterns in each chip did not significantly alter compared to greater variation in GAPDH.