Study On Molecular Polymorphisms Of Cast Gene In Yak And Their Relationships With Meat Quality

M. longissimus dorsi from yaks slaughtered at 2-yr(n=51),3-yr(n=60),4-yr(n=71) were used in this study. Meat quality traits were determined after steaks were aged for 0,1,3,7,14 or 21 d at 4℃, respectively. The meat quality attributes (shear force, dry cooking loss (DCL), moist cooking loss (MCL), pressing loss (PL) and pH) from all 181 animals with six postmortem aging days each were determined, while the chemical composition (moisture, protein and fat) was only determined from 60 yaks (20 individuals per age at harvest) with six aging days each. Part sequences in CAST gene were amplified by 6 primers, and subjected to Single Strand Conformational Polymorphism analysis and DNA sequencing technology. The associations of polymorphic loci with meat quality traits were studied. The aims are to explore the law of interaction of genetic factors and Non-genetic factors in yaks with different genetic basis, to lay foundation for further studying CAST regulation mechanisms in yaks, and to provide molecular genetics data for yak breeding. The results showed as follows:There were 3 mutations detected in the fragment amplified by 1Z primer, including 7-bp insertion/detection in 54-60bp, mutations of Gâ†'A at 108bp and Aâ†'G at 115bp, and a mutation of Aâ†'G was detected at 130bp in the fragment amplified by primer of 6L. The heterozygosity (He) above mutations were 0.2265,0.2707,0.2707 and 0.2990, respectively; and the polymorphism information content (PIC) were 0.2067,0.2067,0.2067 and 0.2547 respectively. The allele+at+54-60M, G at G108A, A at A115G and A at A130G were predominant alleles, respectively. The result of haplotype analysis was that 3 haplotypes, Hap1(+GA), Hap2(+AG) and Hap3(MGA), were detected in 1Z sequence.The variances of meat quality traits in genotype (haplotype), genotype (haplotype)×age, genotype (haplotype)×aging days, genotype (haplotype)×age×aging days were analyzed by least squares linear model of SAS. The results showed that,1) Genotype effects at 108/115 sites were closely related to shear force and fat percentage. The individuals with GG/AA had lesser shear force and higher fat percentage compared to GA/GA. Still interactions of genotype x age at harvest and genotype x age at harvest x aging days were evident for shear force. Genotype GG/AA had lesser shear force compared to GA/GA at 1 and 7 days of aging in 2-yr-old yak and 7 and 14 days of aging in 4-yr-old yak, respectively.2) There was genotype effects on shear force, pressing loss and moisture percentage at 130bp site. The individuals with genotype GA had higher moisture percentage and lesser pressing loss than individuals with genotype AA.3) There was strong evidence (P<0.0001) of genotype x age at harvest x aging days for protein percentage at G108A/A115G sites. Genotype GA/GA had greater protein percentage compared to GG/AA at 1 day of aging in 2-yr-old yak,3 days of aging in 3-yr-old yak and 21 days of aging in 4-yr-old yak, however, genotype GG/AA had greater protein percentage compared to GA/GA at 0 day of aging in 3-yr-old yak.4) There was strong evidence of haplotype x age at harvest x aging days for protein percentage. In 2-yr-old yak, the individuals with Hap2 had greater protein percentage compared to Hapl at 1 day of aging, the individuals with Hapl had lower protein percentage compared to Hap3 at 14 days of aging. In 3-yr-old yak, the individuals with Hapl and Hap3 had greater protein percentage than that with Hap2 at 0 day of aging, and the individuals with Hap2 had greater protein percentage compared to Hap3 at 3 days of aging. In 4-yr-old yak, the individual with Hap2 and Hap3 had greater protein percentage than that with Hapl at 21 days of aging.