Rodents

A variety of special genetic populations of rodents have been developed in order to try to conduct analyses of these complex interactions. These include hybrid populations that carry genes from more than one parental type in predictable proportions, congenic lines that are genetically identical except for differences in a single gene of interest, and genetically selected lines that have been selected for a single trait such as long life, absence of cancer, or high activity rate. Selected populations offer a chance to find sets of genes that influence a trait such as longevity. In the selection process, mice (or rats or nematodes or fruit flies) are mated and then the life spans of the offspring are observed. The longest-lived are mated to one another and so on for many generations. The result is a population of mice with increased longevity. The genetic differences between these animals and their shorter-lived progenitors can then be studied for clues to fundamental aging processes. These genetic factors are likely to be complex and multifactorial. Some genes may be parts of large arrays of genes all of which contribute a small amount to the final expression of a trait. Traits of this type are referred to as quantitative traits. New methods of analysis, such as quantitative trait locus (QTL) analysis, are being developed to cope with this complexity.