Fig. 1.

Collaborative Cross (CC) and Diversity Outbred (DO) mouse resources. The eight founder strains are depicted at the top as color-coded chromosomes. Color-coding for these strains has been agreed upon by the research community and standardized. Founder F1 hybrid offspring are produced from crossing two founder strains and are thus reproducible. Theoretically, there are 102 possible F1 hybrids (including reciprocal crosses). CC strains are inbred (homozygous at most loci) and reproducible. CC F1 hybrids are offspring produced from crossing two CC strains and are thus reproducible. There are many possibilities for CC F1 hybrids. DO mice were derived from CC strains through strict breeding protocols to maintain heterogeneous stocks and are thus not reproducible. Theoretically, there is an unlimited supply of DO mice. They are typically tested as a population of over 100 unique mice. “DO × strain” mice are produced from a DO mouse crossed to an inbred strain. Because DO mice are not reproducible, “DO × strain” mice are likewise not reproducible