Prion gene sequence variation within diverse groups of U.S. sheep, beef cattle, and deer. - Heaton MP; Leymaster KA; Freking BA; Hawk DA; Smith TP; Keele JW; Snelling WM; Fox JM; Chitko-McKown CG; Laegreid WW (Mammalian genome : official journal of the International Mammalian Genome Society, 2003)