Confirmed quantitative trait loci for fatness and growth on pig chromosome4

Quantitative trait loci (QTLs) with large effects on fatness and growth hav e been identified previously on pig chromosome 4 in an intercross between t he European wild pig and Large White domestic pigs. Two F-2 sows, heterozyg ous for the actual chromosome region, were backcrossed to a Large White boa r, and two backcross (BC1) boars were in turn backcrossed to Large White/La ndrace sows. One of the boars was heterozygous for an intact wild pig-deriv ed QTL region, whereas the other carried a recombinant haplotype. A total o f 85 BC2 animals were produced. Phenotypical measurements included daily we ight gain, ultrasonic measurements of fat depth at 70 and 90 kg and several carcass traits. QTL segregation was deduced using 15 markers previously as signed to chromosome 4. Highly significant QTL effects were observed on all fatness traits and on the length of the carcass. A small but significant e ffect on growth was also observed. The results confirm the presence of one or more QTLs on chromosome 4 affecting fatness and growth. There was a good agreement between the estimates of QTL effects in the F-2 and BC2 generati ons. The results from the recombinant sire family allowed us to map the maj or QTL effect distal to the recombination breakpoint. We propose that this confirmed QTL with a major effect on fatness is designated FAT1.