Inbreeding protocol for generating homozygous mutations. G0 mice are bred to germline mutant G1 females, and siblings from both the G1 and G2 generations are crossed. The chance for homozygosity for each G1 mutation is only 1 in 16 in every G3 mouse. Red asterisks indicate mutations originating from the G0 sire; blue asterisks indicate mutations originating in the G1 dam. Star size indicates derivation from an immediate ancestor (large) or from a more remote ancestor (small). Generations (yellow boxes) are aligned. This strategy has the advantage of introducing X-linked mutations into the pedigree, and causes homozygosity for autosomal mutations at a rate 1.39 times greater than would be the case if additional mutations were not introduced by breeding each G0 with a G1 mutant female. Illustration made with assistance of Marie Dauenheimer.