Correlation of observed and expected dipeptides and statistical significance. The mouse proteome was divided into olfactory genes (1,178) and all other genes (33,788) and the frequency of each dipeptide was tabulated. Of the possible 400 dipeptides, 49 can encode the core of the YY1 binding site. A) Observed vs. expected plot of 400 dipeptides (hollow diamonds) as compared to the subset of 49 YY1 binding site core forming dipeptides (filled diamonds). The subset does not deviate from the overall pattern. Pro-Met is indicated as having a much larger observed than expected count. B) Z-score of the observed and expected counts of the subset of YY1 binding site core forming dipeptides. All but three fall within 1 standard deviation of their expected values. Only Ala-Ile, and Pro-Leu deviate significantly from their expected values.