A DIRECTED SEARCH FOR QUANTITATIVE TRAIT LOCI ON CHROMOSOME-4 AND CHROMOSOME-7 IN PIGS

Improvements in the porcine genetic map and availability of resource f amilies to study performance traits in pigs have made it possible to r eexamine previous findings that linked certain traits to genes or chro mosomal regions. Previous studies suggested that chromosomes 4 and 7 m ay be associated with growth and performance traits. To confirm these previous results, an interval mapping-regression approach was used to determine whether quantitative trait loci (QTL) exist in the Iowa Stat e University reference/resource families. Traits measured were birth w eight; body weight at 21 d; weaning weight (weight at 42 d); average d aily gain; backfat at the first, 10th, lumbar, and last ribs and avera ge backfat thickness; loin eye area; meat color; marbling; and firmnes s. The total number of F2 pigs used ranged from 241 to 330 and came fr om five Chinese x American resource families. Five markers (S0001, SW8 71, S0175, S0214, and SW445) were genotyped and mapped on chromosome 4 , and so were 10 markers (S0064, tumor necrosis factor alpha [TNF alph a], S0102, S0078, S0158, S0066, SW304, SW1083, S0101, and S0212) on ch romosome 7. Data were analyzed for each family (breed cross) separatel y and were also pooled. Experiment-wise thresholds were used to determ ine significance. Suggestive evidence of QTL on chromosomes 4 and 7 wa s observed for several traits in pooled and individual family analyses . Suggestive evidence of a QTL with a relatively large effect for aver age daily gain was detected on chromosome 4 in the pooled analysis. Si gnificant(P < .05) evidence for QTL was seen on chromosome 7 for 10th- rib, last-rib, and average backfat thickness in the pooled data set in a region of the chromosome that was near TNF alpha. These results ver ify in part that chromosomes 4 and 7 contain QTL for growth and carcas s traits.