Mouse Models

Mus musculus is the common house mouse.

Its genome is the same size as that of human, with 20 chromosome pairs and 3x10⁹ base pairs. Its life cycle takes two months, and gestation takes 21 days. The physical map of the genome is more complete than that of the human, making it relatively easy to positionally clone a gene identified by mutation. Because it is a mammal, its developmental processes are most similar to that of human. Techniques are available to "knock out" any gene that has been cloned. The entire genome has been sequenced and is available at http://www.informatics.jax.org.

Mice are excellent research models because they are mammals (their biochemical pathways are similar to humans) and their genome sequence is known (99% of human genes are present). Also, it is very easy to control a mouse's environment (diet, climate, etc) and also to control its genetics. Genetically, there are hundreds of inbred strains of genetically identical mice available; also, it is possible to alter gene sequences and expression levels within mice via transgenics and gene targeting.

Term	Overview
Murine	Pertaining to a mouse.
Inbred Strains	Strains of genetically identical mice with a unique set of useful alleles.
Endogenous	Anything naturally present in the in the mouse model, from DNA to tissues.
Exogenous	Anything not naturally present in the murine genome, from DNA to tissues.
Syngenic	Two mice (or strains) are syngenic if they are identical at all loci.
Congenic	Two mice (or strains) are congenic if they are not identical at all loci.
Allogenic	Two mice (or strains) are allogenic if they are from the same species but differ at all genetically.
Transgene	Transgenic mice carry an exogenous gene (the transgene) randomly inserted into the murine genome.
Gene Targeting	Gene targeting (aka targeted mutation) is alteration of an endogenous gene's product or expression.
Induced Mutation	Random and chemically induced point mutations.
Spontaneous Mutations	Spontaneous (not induced) mutations which may interfere with gene products and expression.

Immunologists use inbred strains of genetically identical mice so that organs and tissues can be transplanted between mice without graft rejection. This is because the genetically identical mice have the same MHC molecules. Mating two mice with homozgyous MHCs (for example, H-2^b/b and H-2^k/b) will lead to H-2^b/k heterozygous offspring. The heterozygous progeny can accept grafts from either parent or with each other; however, the homozygous parents cannot accept grafts from their heterozygous offspring.