Identification of quantitative trait loci in beef cattle

The objective of this review is to describe the quantitative trait loci (QTL) identified in beef cattle at the U.S. Meat Animal Research Center (MARC), and to describe the process in which they can be incorporated into animal breeding schemes. Four large half-sib families were developed (two families with 500 offspring each, and two families with an average of 227 offspring) to detect QTL for growth, carcass composition and meat quality traits. Scans in these families, using molecular markers obtained from the bovine linkage map, were done. Regions on chromosomes 2, 3, 4, 5, 6, 8, 13, 15, 16, 27, and 29, were detected to harbor genes associated with these traits. Characterization of the variation of the QTL needs to assessed in outbred populations. Animals from the Germplasm Evaluation Project, developed at MARC, are suitable populations in which this can be accomplished. New marker systems able to be used in high-throughput genotyping systems need to be developed to charaterize the QTL variation in outbred populations. A genomic program is being developed at MARC to produce single nucleotide polymorphisms (SNP) from expressed sequence tags (EST). These molecular markers will provide the means to characterize variation of previously identified QTL. The purpose is to use genomic information to either, identify the alleles of a gene that is producing differences in expression of a trait (Functional genomics), or to use this information in selection schemes supported by marker information (Marker-assisted selection)