NEW APPROACHES TO GENETIC-RESISTANCE IN POULTRY

Single dominant genes code for receptors for penetration of different subgroups of the avian leukosis virus. WERNER HARTMANN has shown that lines of chickens homozygous resistant to Subgroups A and B produce mo re eggs and have lower mortality than comparable lines selected for su sceptibility from the same original populations, showing that breeding for resistance to infection has a similar effect to virus eradication . Breeding for resistance requires exposure of chickens or embryos to virus and selection depends on progeny testing making selection by com mercial breeders difficult. If these genes were molecularly cloned it is likely that co-dominant molecular markers could be devised to detec t resistant phenotypes at an early age without exposure to the virus. Approaches and currently available genome mapping populations are desc ribed that could be used to identify and clone these genes at the mole cular level by map-based cloning approaches. These strategies have gen eral application to using genome mapping and related approaches to ide ntify and clone unknown genes that have a major influence on economic traits.