1. Department of Animal Breeding and Genetics, Swedish University of Agricultural Sciences, Box 7023, 75 007 Uppsala, Sweden
2. Department of Animal Genetics, UMR 0444, LGC, INRA, 31326 Castanet-Tolosan, France
3. Scottish Agricultural College, West Mains Road, Edinburgh EH9 3JG, United Kingdom
4. Institute for Pig Genetics, P.O. Box 43, 6640 AA Beuningen, the Netherlands