Methods and experimental designs for detection of QTL in sheep and goats

Methods for detection of quantitative trait loci (QTL) in sheep are discussed. There is a reasonable coverage of the sheep map with microsatellite markers. Developments in molecular genetic technology have now made available very dense marker maps based on single nucleotide polymorphisms, which will soon be available for sheep. Mapping methods were originally based on linkage analysis, either using crosses of divergent breeds or paternal half sib designs in commercial populations. The size of most QTL experiments are too small to allow precise estimation of QTL with moderate effects. Fine mapping is based on linkage disequilibrium (LD) and methods using LD information have now been developed for mapping of QTL. LD analysis can be based on a random sample of animals from the population and is less dependent on marker information and designed experiments.