Submitted to: Michigan State University Extension
Publication Type: Other
Publication Acceptance Date: 10/20/2010
Publication Date: 10/30/2010
Citation: Comparison of Prion Allele Frequency found in Suffolk and Targhee Sheep. 2010. Phan. J.P., and Mousel, M.R. West Michigan Regional Undergraduate Science Research Conference, Grand Rapids, MI, Oct. 30, 2010. Poster presentation. Interpretive Summary: Genotyping for scrapie resistance is required for some breeds of sheep and by some states for transporting sheep. A R at prion codon 171 has been found to confer resistance to scrapie, and valine at prion codon 136 has been linked to susceptibility to scrapie. We genotyped 133 sheep of the Targhee and Suffolk breeds at the U.S. Sheep Experiment Station for codon 136 and 171. Genotypes for both codons were not different between these groups of Targhee and Suffolk sheep. In unselected populations, genotypic frequency is expected to be 25% AA, 50% AV, and 25% VV. However, in this sample of sheep, the presences of valine was reduced in both breeds (13% AV and 0% VV) because USSES has been selecting against valine. This survey of scrapie genotypes assists in our objective of eliminating all sheep with valine genotypes at USSES.
Technical Abstract: Scrapie is a class of Transmissible Spongiform Encephalopathy that affects sheep and goats. The objective of this study was to compare genotypic and allelic frequencies among USSES Targhee and Suffolk sheep. A total of 122 sheep were genotyped for codon 171 with allele specific primers in 2 separate PCRs and 133 were genotyped for codon 136 with an RFLP. The RFLP was used to detected if an individual had none, one, or two valine allele(s). Valine at codon 136 correlates with a increased susceptibility to scrapie. Chi-square tests were conducted to determine if there were differences in the genotypic and allelic frequencies for the prion codons 171 and 136 due to breed. Hardy-Weinberg tests were performed to determine if the prion codons were in equilibrium. No significant (P>0.05) differences were found between the breeds for genotypic and allele frequencies at either codon. Prion codon 136 was not in Hardy-Weinberg equilibrium for either breed, but 171 was for both breeds. This result is not unexpected because USSES has been performing active selection against valine at condon 136 and only recently began selection for Arginine (R) at codon 171. This study has shown that selection against valine at 136 did not change allelic or genotypic frequencies between Targhee and Suffolk sheep but did change Hardy-Weinberg equilibrium in both breeds, demonstrating that selection can reduce disease-associated alleles.