ABSTRACT
Traditional selection methods using phenotypic information have been successful in improving the profitability of livestock species. However, these methods have biological constraints in that some traits are sex or age limited or difficult and/or expensive to measure. Genetic markers can potentially ameliorate problems with traditional selection methods because they can be measured at any time, in both sexes. Linkage maps of the genomes of all major livestock species have been developed and are publicly available. These maps are the framework for artificial selection aided by markers. In crossbreeding introgression schemes, markers can be used to tag alleles to be introgressed and to speed up the genome recovery of the recurrent breed. Alternatively, marker alleles can be associated with phenotypic variation in recently created synthetic populations. In livestock populations, these methods are being applied at present, using marker alleles for colour, litter size, and disease resistance. Marker assisted selection in non-crossbred populations is more difficult, because associations between marker alleles and trait variation have to be traced within families. However, if markers are used to alter the design of breeding schemes, or to select where previously selection was at random, genetic progress can be increased substantially. Besides the ‘straightforward’ use of markers in selection programmes, markers can be used in quality control programmes, to control the rate of inbreeding, and to utilise non-additive genetic variation.
