Figure 1. Gene expression stability of the candidate reference genes analyzed by the geNorm software based on the principle that gene pairs that have stable expression patterns relative to each other are appropriate reference genes. (A) Average expression stability values (M) of the six remaining reference genes plotted from least stable (left) to most stable (right). (B) Pair-wise variation analysis between the normalization factors NF_n and NF_n+1, to determine the optimal number of reference genes for normalization. The value V5/6 is higher than V4/5; this is due to the inclusion of a relative unstable fifth gene. Increasing variation in this ratio corresponds to decreasing expression stability.