Animal QTLs (Quantitative Trait Locus)

Quantitative trait locus, or QTL analysis, is a modern, genetically based way for breeders to tailor their livestock to the needs of consumers. Researchers performing QTL analysis investigate the role of genes, regionally located on chromosomes, in polygenic traits such as body fat, meat tenderness, or milk production.

The genomes, or entire deoxyribonucleic acid (DNA) contents, of many livestock species have been sequenced. These species include cattle, sheep, chickens, and more. Other important model organisms such as mice and rats have also had their genomes sequenced. Researchers can use the vast information available for comparing and contrasting both different species as well as animals within a species. The ultimate goal of QTL analysis is determining the genetic underpinnings of all traits and characteristics, specifically those that are determined by multiple genes. Such traits are termed polygenic.

DNA is organized in the cell into chromosomes. Roughly speaking, the chromosomes are organized into noncoding DNA and coding DNA which encodes proteins; the region of a chromosome which encodes a protein is called a gene. The hypothesis that forms the basis of QTL theory is that groups of genes near to each other on a chromosome may have a multigene effect on certain polygenic traits. Using sophisticated mathematics and genetic experiments, investigators can examine these gene regions and their relationships to traits. This is the process for QTL mapping. In other words, scientists look at how often particular genes are expressed together in relation (linkage) to specific traits. Breeders can use this information to generate better, more nutritional meat for consumption. For example, pork backfat and cattle milk production have strong QTL linkages.

QTLs can be used to help study many examples of human obesity as well, and in genome scans from 2002, there were reported to be 68 QTLs for obesity in humans.

To aid researchers in their comparisons, there is a website called the Animal QTL database (AnimalQTLdb). As of 2007, the database includes information on pigs, cattle, and sheep, and will expand to include more species.