For many infectious diseases, host resistance may be improved by genetic means, i.e., by breeding for enhanced resistance. This is possible because genetic differences exist between host animals in their resistance to infection, or in the disease impact that infection causes, at many levels. Most obviously, diseases are usually restricted to one or a small number of host species. Additionally, within a species, differences are often seen between breeds in resistance to a specific disease and between individuals within a breed. This article considers the nature and mechanisms underlying variation in disease resistance, reasons why this variation exists despite natural selection, exploitation of this genetic variation for controlling diseases, and future trends in disease genetics.
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