1 International Livestock Research Institute, The Joint Centre for Tropical Livestock Genetics and Health of the University of Edinburgh, International Livestock Research Institute and Scotland's Rural College, Nairobi, P.O. Box 30709-00100, Kenya.
2 Roslin Embryology, (21) EH331QB, Scotland, UK.
3 Department of Biological Sciences, Hunter College, City University of New York, New York, NY, 10065, USA.