1. Nippon Boehringer-Ingelheim Co. Ltd., Yato, Kawanishi-shi 666-01, Japan
2. Lab. of Applied Genetics, Dept. of Animal Resource Sciences, Graduate School of Agriculture and Life Sciences, Univ. of Tokyo, Yayoi, Bunkyo-ku, Tokyo 113, Japan
3. Central Inst., Ajinomoto Co. Ltd., Maeda-machi, Totsuka-ku, Kawasaki-shi 244, Japan