Significant expression variation between genotypes is associated with elevated levels of sequence polymorphism at most types of sites. The y-axis is the per site nucleotide diversity (note: axis scale varies by feature). The pink line indicates the genomic mean nucleotide diversity and yellow lines indicate 95% confidence intervals around the genomic mean. The x-axis represents the level of expression variation between genotypes for the different gene features as named (5'UTR, untranslated region; CPR, core promoter region; NonSyn, nonsynonymous sites; Syn, synonymous sites). P-values from the AOV of expression variation were sorted and grouped into 15 equal sized bins. Bins on the left side of the figure have no evidence of expression variation and bins on the right have the most variably expressed genes. For each bin, blue circles represent the mean nucleotide diversity with standard error bars. Permutation tests examined whether nucleotide diversity was higher within each bin than in a random sample of genes from the genome. The asterisk marks the bin in which an average p-value = 0.05 occurs. To the right of the asterisk, a positive trend is observed in some gene features, suggesting that the positive relationship between gene expression variation and nucleotide polymorphism is not solely confined to the most dramatically differentially expressed genes.