Volcano plot of differences between tissues and corresponding p-values. Differences in expression for each gene is the log2 ratio of tissue mean expression minus grand mean; a twofold difference in expression between tissues is indicated by one unit separation along the x-axis. p-values for differences in gene expression among tissues were calculated using ANOVA, and illustrated as -log(p). A p-value of 10-4 is expressed as 4 on the y-axis, and the α = 0.05 threshold is indicated by the red dashed line (1 - log(0.05) = 1.3).
Whitehead and Crawford Genome Biology 2005 6:R13 doi:10.1186/gb-2005-6-2-r13