Saturation results. A map comparison plot generated using the R/qtl function ’plot.map’ [15,16]. For each of the chromosomes, the original map (left) and the saturated map (right) are plotted. Lines are drawn to connect markers. Markers that exist in one map but not the other are indicated by short line segments. Before plotting, both maps were re-estimated using the R/qtl function ’est.map’. The original map consisted of five chromosomes and 69 markers at an average distance of 7.1 cM. The saturated map consists of the original 69 markers plus 497 expression-based markers at an average marker distance of 0.89 cM.