Two strains of mice which are genetically identical except for a single genetic locus or region are said to be:
Rephrasing the question:
What is the term used for mice that are genetically identical except for one single locus?
Congenic (option 3)
Let’s go through the options one by one.
- Syngenic: genetically identical, or sufficiently identical and immunologically compatible as to allow for transplantation. A syngeneic graft is also known as an isograft.
- Allogenic: genetically different because of being derived from separate individuals of the same species.
- Congenic: two strains/species that differ in only one locus and a linked segment of chromosome.
- Heterogenic: genetically different because of being derived from individuals of a different species
Rogner, U., Avner, P. Congenic mice: cutting tools for complex immune disorders. Nat Rev Immunol 3, 243–252 (2003).