Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 11/15/2004
Publication Date: 11/30/2004
Citation: Casas, E. 2004. The use of genomics to identify genes influencing economically important traits in beef cattle. Proceedings of the First Agrobiotechnology Congress, November 30 to December 4, 2004, Monterrey, Mexico. p. 56-74. Interpretive Summary: The science of genome research in livestock has been the focus of substantial worldwide effort over the last decade. It has been possible to identify chromosomal segments carrying genes affecting production traits. Variation in individual genes having major impact on phenotypes in cattle has been identified. However, the majority of the loci remain unknown except for their approximate position in the cattle genome. Approaches to develop DNA-based tests of genetic merit for important production traits have been slow to develop. The objective of this review was to describe the regions in the genetic material where evidence suggests genes that influence economically important traits reside, the methodology used to develop genetic markers, and their potential use in selection programs. Some discussion centers on how this information will be used to improve economically relevant traits.
Technical Abstract: The development of genetic maps for domestic species and their use for identifying chromosomal regions that harbor genes affecting economically important traits has been the focus of livestock genomic research. Variation within genes having a major impact on the phenotype of the animal, like the form of myostatin that causes double-muscling in cattle, have been identified, but most loci influencing quantitative traits remain unknown. Regions in the genetic material that harbor genes influencing economically important traits are known as quantitative trait loci (QTL). Their approximate locations in the genome and the proportions of variation in the trait that they explain have been estimated. Traits that are sex limited, have low heritability, that are expensive to measure, or that need to be measured in the carcass are best suited for improvement using genomic approaches. Such is the case for carcass composition and meat quality traits, including meat tenderness. Variation in meat tenderness has significant impact on beef consumer's satisfaction, but classical selection techniques have not been effective in eliminating the fraction of animals yielding undesirable palatability traits. Establishing the genetic basis for variation in meat tenderness would likely aid in the development of selection criteria for improving this trait in cattle. Quantitative trait loci associated with the expression of meat tenderness have been identified. A gene known to be involved in postmortem proteolysis resides within the boundaries of a QTL located on chromosome 29. The micromolar calcium-activated neutral protease (CAPN1) gene encodes a cysteine protease, µ-calpain, that degrades myofibrillar proteins under postmortem conditions. Genetic markers, known as single nucleotide polymorphisms (SNP), have been developed in the gene. These genetic markers have been associated with meat tenderness in beef cattle. Their association has been assessed in several cattle populations. Breed evaluations in the future could include genetic marker information to determine the breeding value of the animals with a higher accuracy.