Re: Why are mice used in experiments?

Good question, and there are several reasons. Mice are a popular 
experimental organism with geneticists because they 
1) have fairly large litters, 8-10 is common for some strains, 
2) are small for a mammal and easily housed
3) have a short generation time
4) are easy to work with in general.

These and other considerations are covered on a great web site:
 http://
www.princeton.edu/~lsilver/book/MGcontents.html

As mammals, mice are considered a good but imperfect surrogate for studies 
of human diseases and conditions; their body plan, physiology and genome 
share many features with our own. Traditional breeding methods have 
resulted in the generation of many highly inbred lines of mice which have 
been very useful in studies of the immune system as well as other areas. 
However, the ability to make genetically manipulated mice, aka "designer 
mice", has lead to tremendous advances in understanding the roles of 
individual genes in normal development as well generating animal models for 
testing of therapeutic strategies. Mice are also used in generating very 
specific antibodies, called monoclonal antibodies, which have been very 
valuable tools for research. Although other animals, plants and bacteria 
have been extremely useful in many ways, no other single experimental 
animal offers such a wide variety of uses to science and medicine as a 
mouse.