Mice are the most commonly used mammalian research model with hundreds of established inbred, outbred, and transgenic strains. They are common experimental animals in biology and psychology, primarily because they are mammals, are relatively easy to maintain and handle, reproduce quickly, and share a high degree of homology with humans.
The mouse genome has been sequenced, and many mouse genes have human homologues. In addition to being small, relatively inexpensive, and easily maintained, several generations of mice can be observed in a relatively short period of time as mice reproduce very quickly.
Most laboratory mice are hybrids of different subspecies, most commonly of Mus musculus domesticus and Mus musculus musculus. Laboratory mice can have a variety of coat colors, including agouti, black and albino. Many (but not all) laboratory strains are inbred, so as to make them genetically almost identical.
The different strains are identified with specific letter-digit combinations; for example C57BL/6 and BALB/c. The first such inbred strains were produced by Clarence Cook Little in 1909. Little was influential in promoting the mouse as a laboratory organism.