Fig 3. Characterization of the PTB genes.

(a) Referenced with the genome background, the PTB gene set displayed a significant increase in their intolerance to copy number variations, particularly pronounced to deletion events, but not to duplication events. The same pattern was absent from the term gene set as well as from the GoNL genes. Referenced with the genome background, P values were calculated based on the Wilcoxon rank-sum test. (b) The percentages of lethal, subviable and viable genes in PTB, term and GoNL gene sets. The PTB set was significantly enriched for genes whose mouse orthologs are embryonic essential (i.e. homozygous knockouts displayed embryonic lethal phenotypes), whereas the term and GoNL genes had more viable genes (i.e. homozygous knockouts are viable). The P value was computed using the Fisher’s exact test by comparing the proportion of essential and viable genes in the PTB and term sets. Note that the GoNL set had no lethal and subviable genes.