Mapping the sheep genome: practice, progress and promise.

Over 100 loci have now been mapped on the sheep genome, double that of 3 years ago. Achieved through converging developments in DNA technologies and genetics, this rate of gene mapping is increasing. Its goal is to identify genes for important traits. This will elucidate the biological basis of these traits, paving the way for their manipulation, and accelerate the genetic improvement of sheep and quality of their products by marker-assisted selection. The aim of this review is to provide an introduction to the strategies and methods of gene mapping, highlighting the value of comparative genome analysis. These themes are then elaborated in the description of the ongoing project to map the sheep genome. Opportunities are discussed for the application of the fruits of this research to the understanding and treatment of diseases, and to the development of tools for the genetic improvement of sheep by marker-assisted selection.