"� 1994 Nature Publishing Group http://www.nature.com/naturegenetics � 1994 Nature Publishing Group http://www.nature.com/naturegenetics � 1994 Nature Publishing Group http://www.nature.com/naturegenetics � 1994 Nature Publishing Group http://www.nature.com/naturegenetics � 1994 Nature Publishing Group http://www.nature.com/naturegenetics � 1994 Nature Publishing Group http://www.nature.com/naturegenetics � 1994 Nature Publishing Group http://www.nature.com/naturegenetics "