| Meat tenderness, measured as Warner Bratzler shear force at 14 days postmortem (kg), and marbling score were evaluated in a fine-mapping project exploiting linkage disequilibrium of maternally inherited alleles. First, a genome scan was performed using two paternal half-sib families accounting for known linkage effects. Each family had > 500 offspring produced by mating two Bos taurus taurus x Bos taurus indicus crossbred sires with Bos taurus taurus crossbred dams. Phenotypes were adjusted for effects of sex, days on feed, dam line, year and the probability of inheriting sire QTL alleles. Equal amounts of DNA from the animals in each extreme of the phenotype distributions were combined to form high and low pools. DNA was hybridized to a microarray containing approximately 10,000 SNPs, and the normalized allele intensities were used for allele frequency estimation. Allele frequency differences between high and low pools indicated regions with significant (nominal P<.05) association with marbling on BTAs 2, 3, 4, 5, 6, 9, 10, 11, 14, 16, 23 and 29, and with tenderness on BTAs 6, 10, 11, 14, 15, 16, 23 and 29. Second, areas known previously to contain QTL and displaying significance in the genome scan were validated with individual genotyping. Offspring in Family 1 (136) and in Family 2 (140) were genotyped for SNPs on BTAs 2, 4, 5, 6, 9, 10, 14, 16, 23 and 29. Two areas associated with tenderness (BTA6 and BTA16) were validated with individual genotyping (P<.05); but five areas were false positives (P>.05). Similarly, five areas were validated (P<.05) and seven areas were false positives (P>.05) for marbling. Maternally inherited haplotypes showed association (P<.05) with tenderness on BTAs 2, 6 and 14 and with marbling on BTAs 2 and 14. Last, intragenic SNPs in candidate genes (GRB14 on BTA2 and FABP gene family on BTA14) were discovered and genotyped in the families. GRB14 was not associated with the traits (P>.05), but haplotypes involving the FAPB gene family were associated (P<.05) with marbling. In conclusion, a tenderness QTL was identified on BTA6 and the FABP gene was associated with a marbling QTL on BTA14. |
