Another strategy that has been employed in animals to identify genes related to a given trait is to randomly introduce changes (i.e., mutations) into the animals’ genome. In this approach, mutant lines of mice are produced by injecting male animals with a substance called ethyl-nitrosourea (ENU), which introduces DNA mutations throughout the animals’ genome (De Angelis et al. 2000). These males are then mated to normal female mice, and the resulting F1 mice are tested with extensive screening protocols to identify those with abnormal traits. Mice with the desired trait are then bred to a known mouse strain for genetic linkage analyses to identify the genetic mutation causing the trait of interest. Because the order of the genes is very similar in mice and humans (and other mammals), the location of a mutation identified in a mouse genome may help predict the location of the corresponding gene in the human genome, suggesting potential candidate genes for related traits in humans. The findings of such analyses can then be validated by studying animals in which the identified gene regions have been
