Figure 3.4 Creation of a congenic strain. A highly schematic representation of the relative contributions of donor and recipient alleles at sequential generations of backcrossing. The donor contribution is indicated in white and the recipient contribution is indicated in black with the checkerboard pattern indicative of heterozygous loci. By the tenth generation of backcrossing, the differential segment around the selected locus (Figure 3.6) will represent the major contribution from the donor genome.