Biological principles of heredity of and resistance to disease.

Understanding the biological principles of disease heredity and resistance to disease is a prerequisite for the incorporation of these factors into multi-trait breeding programmes. Mutations represent an evolutionary aspect of disease. The author reviews patterns of Mendelian inheritance and possible causes of non-Mendelian inheritance, such as multifactorial inheritance, expansion of trinucleotide repeats, mitochondiral inheritance and genomic imprinting, in relation to diseases of domestic animals. Host-pathogen interactions underlie genetic variability in resistance to disease. Infectious pathogens endowed with a high potential for evolutionary change use this potential to evade various host defence mechanisms. This interaction may have a competitive or co-evolutionary character. The host immune system copes with the variability of pathogens by using the potential of genetic diversity of lymphocytes in immunoglobulin, T-cell receptor and major histocompatibility complex genes. Possible mechanisms for maintenance of this diversity are discussed in the context of selection for disease resistance.