Histogram of the <i>Z</i>-score for <i>Pr</i>(link|<i>d</i>) for each pair of genes and their respectively encoded proteins.

<p><i>d</i> is the Euclidean distance between pairs of genes in the space of the first two PCA components of codon bias, and <i>Pr</i>(link|<i>d</i>) is the conditional probability of having a link in the PIN between two proteins given that their encoding genes are localized within a distances <i>d</i> in the PC1-PC2 plane. The <i>Z</i>-score is obtained as <i>Z</i>[<i>Pr</i>(link|<i>d</i>)] = [<i>Pr</i>(link|<i>d</i>) − 〈<i>Pr</i>(link|<i>d</i>)〉_Ω]/<i>σ</i>_Ω[<i>Pr</i>(link|<i>d</i>)]. The gray dashed lines mark the significance interval of ±3<i>σ</i>.