genetics Genetics is the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinian friar wor ...

, two

organism In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and ...

s that differ in only one

locus Locus (plural loci) is Latin for "place". It may refer to: Entertainment * Locus (comics), a Marvel Comics mutant villainess, a member of the Mutant Liberation Front * ''Locus'' (magazine), science fiction and fantasy magazine ** ''Locus Award' ...

and a linked segment of chromosome are defined as congenic. Similarly, organisms that are coisogenic differ in one locus only and not in the surrounding chromosome. Unlike congenic organisms, coisogenic organisms cannot be bred and only occur through spontaneous or targeted mutation at the locus.

Generating congenic strains

Congenic strains are generated in the laboratory by mating two inbred strains (usually rats or mice), and back-crossing 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 back-cross 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 or 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 five back-cross generations, through the selection at each generation of offspring that not only retain the desired chromosomal fragment, but 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 A microsatellite is a tract of repetitive DNA in which certain DNA motifs (ranging in length from one to six or more base pairs) are repeated, typically 5–50 times. Microsatellites occur at thousands of locations within an organism's genome. ...

markers, but now, more commonly,

single nucleotide polymorphism In genetics, a single-nucleotide polymorphism (SNP ; plural SNPs ) is a germline substitution of a single nucleotide at a specific position in the genome. Although certain definitions require the substitution to be present in a sufficiently larg ...

markers (SNPs). The process can be further aided by the

superovulation Controlled ovarian hyperstimulation is a technique used in assisted reproduction involving the use of fertility medications to induce ovulation by multiple ovarian follicles. These multiple follicles can be taken out by oocyte retrieval (egg colle ...

of females, to produce many more eggs.

Generating congenic strains

See also

Notes and references

Further reading