中国荷斯坦奶牛κ-酪蛋白基因第四外显子多态性与产奶性状的关联分析

Genetic polymorphism of κ-casein gene exon 4 and its correlation with milk production traits in Chinese Holstein cows

以544头中国荷斯坦奶牛为研究对象,以κ-酪蛋白基因为产奶性状的候选基因,扩增779bp的片段,结合测序结果采用PCR-RFLP方法来检测κ-酪蛋白基因3个位点的多态性。结果在exon4的第10891bp、10927bp和10988bp处分别发生了T/C、C/A错义突变和G/A同义突变,据此分别选择了TaqⅠ、HindⅢ、PstⅠ等3种限制性内切酶检测了其多态性。发现3个位点的A、B等位基因在群体中都有分布,且处于低度多态;A和B等位基因的频率分别为86.03%和13.97%;AA,AB和BB基因型频率分别为73.71%,24.63%和1.66%;χ2适合性检验表明,该群体在这3个位点的突变达到Hardy-Weinberg平衡状态(P>0.05);BB和AB基因型个体乳脂率显著高于AA基因型个体(P<0.05),AB基因型个体脂蛋白比显著高于AA基因型个体(P<0.05),但不同基因型对产奶量和乳蛋白率没有显著影响;3个位点的酶切多态性在所研究群体中是紧密连锁的。说明在中国荷斯坦奶牛群体中,κ-酪蛋白B等位基因可作为改良奶牛乳脂率性状的分子遗传标记。

κ-casein gene was regarded as a candidate gene for milk production traits of cows. In this study, a 779 bp fragment of r-casein gene of Chinese Holstein was amplified by polymerase chain reaction （PCR）, the polymorphisms of three loci of κ-casein gene were detected by PCR-RFLP with restriction endonuclease Taq Ⅰ, Hind Ⅲ, Pst I. After sequencing, TIC single nucleotide polymorphism （SNP） was identified at nucleotide 10 891, C/A SNP was identified at nucleotide 10 927 and G/A SNP was identified at nucleotide 10 988 in exon4 of κ-casein gene. Both alleles （A and B） of three loci were found in the population that showed low polymorphism. The gene frequencies of A and B were 86.03% and 13.97%, respectively. The genotype frequencies of AA, AB, and BB were 73.71%, 24.63%, and 1.66%, respectively. Statistical results of X2 test indicated that three polymorphism sites in the population fitted with Hardy-Weinberg equilibrium （P 〉 0.05）. Meanwhile, the effect of polymorphism of κ-casein gene on milk production traits was analyzed. The results indicated that in the three loci, the different genotype of κ-casein gene had no significant influence on milk yield and milk protein percent （P 〉 0.05）. The cows with genotypes BB and AB showed higher milk fat percent than those with genotype AA （ P 〈 0.05 ） ; with genotype AB showed higher fat protein ratio than those with genotype AA （ P 〈 0.05 ）, The polymorphism of the three loci in the experimental population is closely linked. The conclusion is that κ-casein B allele can be used as the molecular genetic markers of modifying milk fat percent in Chinese Holstein cows.