1. Department of Animal Sciences, University of Wisconsin-Madison, Madison, WI 53706.
2. Department of Dairy Sciences, University of Wisconsin-Madison, Madison, WI 53706.
3. WiCell Research Institute, Madison, WI 53707.
4. University of Wisconsin-Madison Biotechnology Center, Madison, WI 53706.
5. Laboratory of Genetics, The Salk Institute for Biological Studies, La Jolla, CA 92037.