Congenic

In genetics, two organisms that differ in one locus are defined as congenic or coisogenic.

Congenic Strains
Congenic strains are generated in the laboratory by mating two inbred strains, and backcrossing the descendants 5-10 generations with one of the original strains, known as the recipient strain. Typically selection for either phenotype or genotype is performed prior to each backcross generation. In this manner either an interesting phenotype, or a defined chromosomal region assayed by genotype is passed from the donor strain onto an otherwise uniform recipient background. Congenic mice can then be compared to the pure recipient strain to determine whether they are phenotypically different if selection was for a genotypic region, or to identify the critical genetic locus, if selection was for a phenotype. Congenic strains are discussed in detail in Lee Silver's online book Mouse Genetics: Concepts and Applications

Notes and References
congenisch