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 Augustinians, Augustinian ...

, two

organism An organism is any life, living thing that functions as an individual. Such a definition raises more problems than it solves, not least because the concept of an individual is also difficult. Many criteria, few of them widely accepted, have be ...

s that differ in only one locus 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 Sequence motif, 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 organ ...

markers, but now, more commonly,

single nucleotide polymorphism In genetics and bioinformatics, 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 ...

markers (SNPs). The process can be further aided by the superovulation of females, to produce many more eggs.

Generating congenic strains

See also

Notes and references

Further reading