Figure 2

Ranking of the reference genes and pair-wise variation by geNorm. Candidate reference genes were ranked according to the average expression stability in intervertebral disc organ culture of Sprague-Dawley rat (a), New Zealand White rabbit (b), and combined species (c). Pair-wise variations (V_n/n+1) were calculated to determine the minimum number of reference genes. The cutoff value was set at 0.15. The optimal variation is marked with a star (*).