The use of marker-assisted selection in animal breeding and biotechnology.

Improvement of livestock has focused on the selective breeding of individuals with superior phenotypes. With the development of increasingly advanced statistical methods that maximise selection for genetic gain, this simple approach has been extremely successful in increasing the quantity of agricultural output. However, information now available on the organisation and functioning of the genome could be used in breeding programmes to improve a range of traits. Many traits are under the control of several genetic loci, each of which contribute to the variation in the trait and hence are called quantitative trait loci (QTL). While genetic markers for QTL that are linked to the trait gene could be used to choose animals for selective breeding programmes, the most effective markers are the functional mutations within the trait genes. Strategies to identify markers for traits and the application of these markers are described by reference to examples of loci that control a range of different traits.