(a) Structure of the cardiac actin gene, Actc1, and the tandem duplication (dotted box) in strains with the D haplotype. (b) Actc1 expression in heart is controlled by a strong cis-eQTL that corresponds precisely to the location of the Actc1 gene on Chr 2 at 114 Mb (solid red triangle). X-axis represents the megabase coordinate on Chr 2 while the y-axis represents the LOD linkage score. Thin horizontal lines provide genome-wide significance thresholds (upper red line at P<0.05 and lower grey line at P<0.63). (c) Mean expression of Actc1, Acta1 and Acta2 highlights the partial compensation for B haplotypes (green, n=24) and D haplotypes (blue, n=12). Expression values are normalized on a log2 scale (mean±s.e.m.). Heart expression data is from GeneNetwork data set GN485 (EPFL/LISP BXD CD-HFD Heart Affy Mouse Gene 2.0 ST (Jan14) RMA). (d,e) Both skeletal muscle and smooth muscle actins (Acta1 and Acta2) also map precisely to Actc1.