Quality Assessment and Normalization. (A) Ratio values (M = Log2(R/G), R = Red channel, G = Green channel) versus average values (A = Log2(R×G)/2) for one placenta sample. Dots represent spots in the microarray. Crosses correspond to control spots. Lines represent the tendency for each block (print-tip) in the microarray. (B) Control assay, two reference mRNA aliquots were hybridized changing the dye color only. Symbols as in (A). (C) Normalized data from (A). (D) Normalized data from (B). Control spots removed in (C) and (D).