Animal Genomics and Improvement Laboratory, BARC, Agricultural Research Service, USDA, Beltsville, Maryland 20705 USA
Traditional genetic selection programs based on pedigree and performance information have been used to improve livestock populations for decades. The introduction of high-density single nucleotide polymorphism genotyping about 10 years ago supported increased rates of gain through more accurate prediction of genetic merit earlier in life. Recent continued technological advances enable the routine use of genetic engineering and gene editing tools in livestock research and, increasingly, production systems. Livestock geneticists have responded by proposing new breeding schemes that combine traditional selection methodology with these new tools to substantially increase rates of genetic gain while reducing harmful effects due to decreased heterozygosity. Genetic improvement strategies based on gene drives have the potential further increase rates of gain but pose risks that may not be acceptable to the public. Intense debate about the use of these technologies in the animal food chain are being driven by regulatory agencies and consumer advocates, and it is not clear if genetically modified animals will be acceptable to consumers. This review focuses on the application of genetic engineering and genome engineering tools to livestock population improvement through the management of genetic load and the promotion of desirable alleles in the population associated with both single-gene and complex traits. Limitations of the current technology, such as limited knowledge of true causal variants, are discussed, as are regulatory and consumer acceptance issues.
Keywords: gene editing, genome engineering, quantitative traits, recessive disorders