Genetics of Disease Resistance

Abstract

A role for genes of the host in resistance or susceptibility to specific diseases is generally accepted by those who work with cattle but difficult to document scientifically. The necessary scientific experiments are expensive and plagued with difficulties in design. Several such experiments are in place, however, each with the potential to not only document the existence of such genes but to either identify the genes or to locate them on chromosomes relative to mapped markers. The "candidate gene" approach is to find genetic polymorphism in and around genes with a known or suspected involvement in host-pathogen interactions and to look for associations of allelic forms of the gene with clinical response. The alternative is a "genomic" approach in which crosses made to segregate the response to pathogens and a battery of markers, spanning as much of the genome as possible, are followed to look for genetic linkage of the trait with a specific marker. The latter approach will be facilitated by a complete marker map of the bovine genome. The complete marker map is rapidly becoming a reality. The rapid development of microsatellite and other hypervariable markers and the availability of a common set of reference families for linkage analysis has almost achieved the goal of a 20 cM linkage map. Immediate needs for development are (1) markers to anchor physical maps to linkage maps, (2) resource families segregating economic trait loci, and (3) chromosome-specific libraries to develop densely saturated linkage maps over genomic regions shown to contain economic trait loci. These needs are being addressed by organized national and international programs, particularly in the USDA's NAGRP program and the latest European genome effort called BovMap.