Breeding schemes for the generation of GRP populations. Different colors represent the genotypes of the respective inbred founder strain chromosomes. (A) For a standard RI GRP, two founder strains are crossed to generate an F1 population. F1 progeny are then crossed to generate F2 mice, followed by inbreeding to establish a panel of RI strains. (B) High diversity mouse GRPs were developed by crossing eight inbred founder strains (all possible founder cross combinations were generated). The progeny were crossed to develop the CC panel of RI strains, which combine high diversity with reproducibility. CC mice were then outbred to generate the DO panel, which lends itself to greater phenotypic variation, and higher resolution mapping given accumulated recombination events.