Figure 1.

Generation of recombinant inbred (RI) strains. The progenitors of RI strains are animals of two inbred strains that carry different forms (i.e., alleles) of polymorphic genes (indicated by the colors blue and red). For each animal, the figure shows one chromosome pair in which one chromosome is inherited from each parent. In an inbred strain, each animal has two copies of the same allele of each gene, meaning they are homozygous at each locus. Many alleles do not differ between strains, however, and the white areas on the chromosomes represent those regions that are not polymorphic.