Mice are small, easy to keep, and complete a generation in only ten weeks. They are also rather closely related to human beings.

As a mammal, a mouse is rather closely related to a human being. However, it is small, easy to keep, and completes a generation in only ten weeks. It shares more genes, anatomy, and physiology with us than the simpler model systems – bacteria, worms, or flies. Many laboratory strains of mice have been inbred to be genetically identical, which makes it easier to see the effects of an experimental treatment or change in a single gene. A method called homologous recombination allows scientists to precisely replace virtually any mouse gene with a mutated copy of the same gene or a related gene from another organism. A “transgenic” mouse is usually created by injecting a foreign gene into embryonic stem cells and then implanting the manipulated embryos into a surrogate mother. Transgenic mice carrying human disease genes are models for Huntington’s disease, sickle cell anemia, Alzheimer’s disease, and many cancers.

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