Molecular genetics methods are promissing tools for improving production and disease resistance traits of the livestock. The methods of DNA analysis enable the direct identification of genotype and are very useful in following breeding activities: - identification of QTLs (quantitative trait loci), - marker assisted selection (genotyping for genetic markers linked to productive traits), - parentage control, - embryo sexing. The genetic tests are also used for identification of genetic disorders caused by a single point mutation as well as chromosome aberrations. Analysis of DNA polymorphism makes possible the estimation of inbreeding within a population and genetic distance between the populations as well as changes in gene frequency caused by the selection.
Disease resistance of the animals may be improved using both, the conventional (marker assisted selection) and genetic engineering methods. Marker-assisted selection (MAS) can use genetic markers as indices of resistance to diseases. The markers may be devided into exterior traits (e.g. udder and teat conformation – mastitis), determined by serological tests (erythrocyte antigens - leukaemia., MHC antigens - mastitis, leukaemia and tuberculosis in cattle, nematode infection in sheep, Marek's disease in poultry) and molecular analysis of DNA (loci encoding intestinal receptor for K88 and F18 Eschericha coli, MHC genes - mastitis and leukaemia in cattle). Conventional methods should be preferable in improvement of existing resistance mechanisms while the genetic engineering methods (e.g. transgenesis) can be used to introduce into livestock genomes the genes controlling resistance to diseases.