Congenic
Encyclopedia
In genetics
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....

, two organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...

s that differ in one locus
Locus (genetics)
In the fields of genetics and genetic computation, a locus is the specific location of a gene or DNA sequence on a chromosome. A variant of the DNA sequence at a given locus is called an allele. The ordered list of loci known for a particular genome is called a genetic map...

 are defined as congenic or coisogenic.

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. The process can be aided by the superovulation of females, to produce many more eggs . 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
Single nucleotide polymorphism
A single-nucleotide polymorphism is a DNA sequence variation occurring when a single nucleotide — A, T, C or G — in the genome differs between members of a biological species or paired chromosomes in an individual...

markers (SNPs)

Further reading

Congenic strains are discussed in detail in Lee Silver's online book Mouse Genetics: Concepts and Applications:http://www.informatics.jax.org/silver/frames/frame3-3.shtml
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