Alternative splicing events were classified (see Materials and methods) into 7 types: alternative 3’ splice (A3, blue), alternative 5’ splice (A5, purple), alternative first exon (AF, orange), alternative last exon (AL, brown), mutually exclusive exons (MX, black), retained intron (RI, green), and skipped exon (SE, dark red). All events were quantified in each sample for percent spliced in (PSI). (A) Number of alternative splicing events of each type (solid color), and number of genes affected by these events (light color). (B) Example of partial exon skipping in Colq gene. DBA shows the complete inclusion of the exon (therefore PSI = 1), while in C57BL/6 there is partial exon skipping (PSI = 0.78). (C) Number of alternative splicing events with and without local QTL signal (solid and light color respectively). (D) Alternative splice QTLs are mapping to the same chromosome, for all types of events, indicating that most of genetic regulation is by local (and likely cis acting) variants. (F) Distance between most significant SNP for each event and gene start. The largest effect is typically within 1 Mb of the gene. (G) An example of mapping of mutually exclusive exon event in Nnat gene mapping to SNP rs32019082. (E) Distribution of all PSI values of each event type in all samples.