Figure 1.—

Experimental design for the reciprocal introgression of the X chromosome. (A) Three targeted X chromosome congenic genotypes (proximal, center, and distal) for experiment 1 and experiment 2. For each male genotype, the genetic composition of three autosomes, the X chromosome, and the Y chromosome is given. White chromosomes represent domesticus^LEWES and black chromosomes represent musculus^PWK. For both experiments the mitochondrial DNA derives from musculus^PWK. (B) Example of congenic strain construction for introgression of the distal musculus^PWK X chromosome over 10 generations of breeding. Expected levels of heterozygosity for each generation are given in parentheses; at the N₁₀ generation the genomic background will be ∼99.8% homozygous for domesticus^LEWES alleles.