A chromosome substitution or consomic strain is an inbred strain with one of its chromosomes replaced by the homologous chromosome of another inbred strain. The C57BL/6J and C3H/HeJ inbred strains were selected for this consomic because they differ in their susceptibility to infectious disease, specifically Chlamydia trachomatis. Consomic strains can accelerate quantitative trait loci identification and mapping. The Jackson Laboratory 2024, used with permission.