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Rat Strain Definitions

Strain Type


No. of Strains

inbred An inbred strain has a defined background. It has been mated brother x sister for 20 or more consecutive generations, hence these can be traced back to their common ancestors.  Any individual inbred rat’s genome is understood to have on average only 0.01 residual heterozygosity (excluding any genetic drift).  Therefore, members of an inbred strain are regarded for most purposes as genetically identical. An inbred strain is designated by a brief symbol made up of upper case, roman letters or a combination of letters and numbers. Examples of some inbred strains are: ACI, FHH, BN. 670
mutant These are animals in which there is a structural change in the DNA. This could be an insertion, deletion or chromosomal rearrangement generated spontaneously or by artificial methods. 534
consomic Consomic strains are produced by repeated backcrossing of a whole chromosome onto an inbred strain. 85
congenic Congenic strains are produced by repeated backcrosses to an inbred strain with selection for a particular marker from the donor strain. 917
transgenic These animals have a DNA fragment that has been stably introduced into the germline which can be generated by a random insertion into the genome. 139
coisogenic These are inbred strains that differ at only a single locus through mutation occurring in that strain. 13
recombinant inbred These are formed by crossing two inbred strains, followed by 20 or more consecutive generations of brother and sister mating. 128
segregating inbred These are inbred strains in which a particular allele or mutation is maintained in a heterozygous state. 13
advanced intercross line Advanced intercross strains are made by producing an F2 generation between two inbred strains and then intercrossing in each subsequent generation. 3
hybrid These are progeny of two inbred strains, crossed in the same direction, and are genetically identical. 4
conplastic Conplastic strains are strains in which the nuclear genome from one strain has been crossed onto the cytoplasm of the other (the mitochondrial donor is always the female parent) during the backcrossing program. 1
outbred These animals are genetically undefined, that is, these are bred with animals that are unrelated to each other, and not bred with siblings or close relatives. 46
mixed inbred A mutant strain, incipient or inbred, derived from more than two progenitor strains or having genetic contribution from an unknown source is considered a mixed inbred strain.
recombinant congenic These strains formed by crossing two inbred strains, followed by a few (usually two) backcrosses of the hybrids to one parental strain.
substrain An inbred strain can be divided into substrains. Substrains are formed when genetic differences are established by residual heterozygosity at the time of branching, mutation or contamination. These are also formed when branches are separated before F40 or when a branch is maintained separately from other branches for 20 or more generations. Genetic differences, which are discovered from contamination during breeding, may also lead to substrains.  Substrains may give rise to further substrains by continued maintenance by a different investigator.
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