Polydactyl Pigs: Theres More to the Story Than Just Extra Toes
Iowa State University Animal Industry Report 2006. Several pigs expressing a polydactyl (extra toes) phenotype were identified in the ISU purebred Yorkshire herd. Sires, dams, and littermate sibs to the polydactyl pigs were retained in the herd and planned matings were designed to enlarge the population. In addition to creating 12 pigs with either extra toes or dewclaws, the population also had an extremely high number of stillborn and mummified pigs. Furthermore, this population also showed differences in growth and reproduction. Multiple genes have been implicated in causing extra digits in several other species. Using comparative genomics as a guide many of these genes were expected to map on pig chromosome 18. Pig chromosome 18 is the smallest pig autosome on which there has been limited research. Candidate genes on pig chromosome 18 were mapped to ensure their location using Iowa State Universitys Berkshire by Yorkshire resource population. Once chromosomal locations were confirmed for each candidate gene, genotypes were obtained for each gene on all pigs in the polydactyl population and were used by a complex statistical method (Elston-Stewart algorithm) to calculate the likelihood that the gene caused the polydactyl phenotype.