Linear animals or inbred strains are animals of a particular species which are nearly identical to each other in genotype due to long inbreeding. Mating of brother-sister pairs for 20 generations will result in lines that are roughly 98% genetically identical, usually sufficient to be considered an inbred strain (compare to identical twins or clones which are 100% genetically identical, or fraternal twins or normal siblings, which are roughly 50% identical). Such animals are frequently used in laboratories for experiments where for reproducibility of conclusions all the test animals should be as similar as possible.