Distribution of 5'UTR intron positions relative to the start and end points of the associated UTRs. Pink bars represent the observed positions of 5'UTR introns relative to the end of the 5'UTR (i.e. the start codon ATG). Black bars represent the observed positions of 5'UTR introns relative to the beginning of the 5'UTR. The line represents the random model expected values (identical for both the black and pink bars). The positions are the intron excision points in the spliced transcript. The x-axis shows the mid-points of the length range that each bar covers (e.g. if the range is 41–60 nucleotides, the mid-point is 50.5, bin size = 20 nucleotides).