Fig. 1: Three types of quantitative trait loci (QTLs); gene eQTL, isoform eQTL and i-rQTL.

a Gene A has 2 isoforms, isoform 1 and isoform 2. A locus affecting the expression level of gene A is defined as gene eQTL. A locus affecting the expression level of isoform 1 and/or 2 is defined as i-eQTL (isoform eQTL). A locus affecting the isoform ratio of isoform 1 and/or 2 is defined as i-rQTL (isoform ratio QTL). b An example of gene having both gene-eQTL and i-eQTL effects but not i-rQTL effect (the upper panel) and that having both i-eQTL and i-rQTL effects but not gene-eQTL effect (the lower panel). c The three types of QTLs are not independent but overlapping concepts. †and ‡ indicate the genes in the upper and lower panels of b, respectively. d Data preparation and processing from 6 peripheral blood cells for the QTL analyses. e Distributions of top QTL variants relative to the gene body. In the figure, the length of the gene body is 30,000 bp, which is the average length of all isoforms.