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Abstract
Extract
Genetic variation, whether due to the fortuitous recombination of genes at meiosis and fertilization, or to mutation, is the means of evolution and the tool of the animal breeder. Along with favourable variations of the genome, there may be unfavourable variations, some so unfavourable as to result in clinically apparent disease. Therefore, it is biologically normal for genetically induced diseases to occur in all species, races or breeds. Such disease may be caused by structural or functional defects of many kinds and it is important to differentiate these from similar diseases induced by environmental agents. Although the cost of inherited diseases to the national economy may be lower than that caused by diseases of infectious or nutritional origin, inherited diseases may be economically important, particularly to individual breeders. Certain genetically caused diseases may spread insidiously through a breed until they are difficult to control economically. It is therefore highly desirable that diseases with a genetic basis be recognized at an early stage and control measures instigated. Apart from the economic aspects of inherited diseases, they may be important as experimental models for the study of similar diseases in man.