Microarray profiling data distributions. The distribution of p-values for differential gene expression comparing articular cartilage to repair tissue using 8 replicates (4 left legs and 4 right legs from 4 horses) is demonstrated in a histogram (A); the column at the far left are those differentially expressed at p < 0.01 and represents 4269 probe sets, or 45.6% of the microarray. (B) A volcano plot illustrates the divergent distribution of probe sets between normal articular cartilage and repair tissue. Log2-fold change differences of transcript abundance are represented across the horizontal axis; fold changes greater than 2-fold are located outside of the vertical dotted lines. Significance (-log10 p-value) is represented on the y-axis with p < 0.01 located above the blue horizontal line. Probe sets within the blue shaded region have a fold change ≥ 2 at p < 0.01 in normal articular cartilage relative to repair tissue. Probe sets within red shaded region have a fold change ≥ 2 at p < 0.01 in repair tissue relative to normal articular cartilage.