Congenic - Generating Congenic Strains

Generating Congenic Strains

Congenic strains are generated in the laboratory by mating two inbred strains (usually rats or mice), 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/rats 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.

Speed congenics can be produced in as little as 5 back cross generations, through the selection at each generation of offspring that not only retain the desired chromosomal fragment, but that also 'lose' the maximum amount of background genetic information from the donor strain. This is also known as 'Marker Assisted' congenics, due to the use of genetic markers (typically microsatellite markers, but now, more commonly, single nucleotide polymorphism markers (SNPs). The process can be further aided by the superovulation of females, to produce many more eggs.