ABSTRACT
This chapter explains the main features of modifier genes and approaches to their study using the examples of cancer modifier genes and genes that modify T-cell activation and response to infection, to a considerable extent based on own work. It provides an overview the status of mapped cancer quantitative trait loci (QTLs), both in the recombinant congenic strains model and in other models. The multiplicity of genes affecting common diseases such as cancer, infectious and autoimmune diseases, renders the mapping of the QTLs difficult, as each of the multiple genes accounts, by definition, for only a small part of genetic variance. Susceptibility to tumors in different organs usually exhibits a different strain distribution pattern, indicating that different subsets of genes affect the tumor susceptibility in each organ. However, the complex genetics, with possibly multiple loci on chromosome 19 and genetic interactions involved, show the limitations in the use of Colon cancer susceptibility for dissecting multigenic traits.
