Previously genomic scans revealed quantitative trait loci (QTL) on porcineChromosome 8 (SSC8) as significantly affecting the number of corpora lutea (CL)in swine. In one study, statistical evidence for the putative QTL was found inthe chromosomal region defined by the microsatellites (MS) SW205, SW444, SW206,and SW29. A Yeast Artificial Chromosome library was screened by using thecorresponding primers for clones containing these MS by PCR. From five positiveYAC clones, 10 additional MS were isolated and mapped to SSC8 with theINRA-University of Minnesota porcine Radiation Hybrid (IMpRH) panel. The geneticmap position of the QTL has been refined by addition of these 10 markers. TheQTL evaluation included pedigrees of F2-intercross Meishan x Yorkshire design,with phenotypic data of 108 F2 female offspring and genotypic data for 29 MSmarkers on SSC8. The analysis was performed by using the least squaresregression method. The calculated QTL effect for CL obtained by the multilocusleast squares method showed a maximum test statistic (F value = 13.98) atposition 99 cM between three MS derived from YACs containing SW205 and SW1843spanning an interval of 7.1 cM. The point-wise (nominal) P-value was 5.21 x 10-6corresponding to a genome-wide P-value of 0.009. The additive QTL effectexplained 17.4% of the phenotypic variance.