Cloning and characterization of highly polymorphic porcine microsatellites

A size-fractionated (200-400 bp) porcine genomic library was screened with the dinucleotide motifs (TG)n and (TC)n. The number of TG- and TC-positive clones was 83 and four, respectively, implying that the former motif is more frequent in the porcine genome, as previously reported in other species. Twenty-six TG-clones were sequenced, and the number of repeats varied between 16 and 42 with different compositions of the repetitive sequences; 17 clones had a perfect stretch of TG-repeats, four had imperfect stretches, and five had a compound structure with TG-repeats followed by TC-repeats. Primers for DNA amplification using the polymerase chain reaction (PCR) were synthesized for six loci. Ten unrelated individuals (two wild boars and eight domestic pigs of the Swedish Yorkshire breed) were screened for microsatellite polymorphism. All six microsatellite loci were polymorphic with two to seven alleles and observed heterozygosities in the range of 0.42-0.84; the inheritance of the observed polymorphism was confirmed by family studies. The characteristics of microsatellites make them highly suitable as genetic markers, and these microsatellites were isolated as a part of a pig gene mapping project.