Thaller G, Krämer W, Winter A, Kaupe B, Erhardt G, Fries R
Lehrstuhl für Tierzucht, Technische Universität München, 85354 Freising, Germany.
J Anim Sci. 2003 Aug;81(8):1911-8. doi: 10.2527/2003.8181911x.
Various QTL mapping experiments led to the detection of a QTL in the centromeric region of cattle chromosome 14 that had a major effect on the fat content of milk. Recently, the gene encoding diacylglycerol O-acyltransferase (DGAT1) was proposed to be a positional and functional candidate for this trait. This study investigated the effects of a nonconservative lysine to alanine (K232A) substitution in DGAT1, which very likely represents the causal mutation, on milk production traits. Existing granddaughter designs for Fleckvieh and German Holstein, the two major dairy/dual-purpose breeds in Germany, were used to estimate allele frequencies and gene substitution effects for milk, fat, and protein yield, as well as fat and protein content. A restriction fragment length polymorphism assay was applied to diagnose the K232A substitution in DGAT1. Estimates of the allele frequencies for the lysine-encoding variant were based on maternally inherited alleles in sons and amounted to 0.072 for Fleckvieh and 0.548 for German Holstein. Effects of DGAT1 variants on content traits were pronounced; estimates of the gene substitution effect for the lysine-encoding variant were 0.35 and 0.28% for fat content and 0.10 and 0.06% for protein content in Fleckvieh and German Holstein, respectively. Conversely, negative effects of the lysine variant of -242 to -180 kg for Fleckvieh and -260 to -320 kg for German Holstein were revealed for milk yield from first to third lactation, resulting in enhanced fat yield of 7.5 to 14.8 kg in Fleckvieh and 7.6 to 10.7 kg in German Holstein. For protein yield, however, mainly negative effects of -3.6 to 0.2 kg in Fleckvieh and -4.8 to -5.2 kg in German Holstein were observed. Pearson correlations between residuals of milk yield and content traits were decreased when omitting DGAT1 effects in the analysis, thereby indicating that DGAT1 contributes to negative correlations between these traits. Molecular tests allow for the direct selection among variants; however, the benefits of the alternative alleles depend on economic weights given to the different milk production traits in the breeding goal.
各种数量性状基因座（QTL）定位实验导致在牛14号染色体着丝粒区域检测到一个对牛奶脂肪含量有重大影响的QTL。最近，有人提出编码二酰甘油O-酰基转移酶（DGAT1）的基因是该性状的位置和功能候选基因。本研究调查了DGAT1中一个非常可能代表因果突变的赖氨酸到丙氨酸（K232A）非保守替换对产奶性状的影响。利用德国两个主要奶牛/兼用型品种弗莱维赫牛和德国荷斯坦牛现有的孙女设计来估计牛奶、脂肪和蛋白质产量以及脂肪和蛋白质含量的等位基因频率和基因替换效应。应用限制性片段长度多态性分析来诊断DGAT1中的K232A替换。编码赖氨酸变体的等位基因频率估计基于儿子中母系遗传的等位基因，弗莱维赫牛为0.072，德国荷斯坦牛为0.548。DGAT1变体对含量性状的影响显著；弗莱维赫牛和德国荷斯坦牛中编码赖氨酸变体的基因替换效应估计脂肪含量分别为0.35%和0.28%，蛋白质含量分别为0.10%和0.06%。相反，对于第一至第三胎产奶量，发现弗莱维赫牛赖氨酸变体的负面影响为-242至-180千克，德国荷斯坦牛为-260至-320千克，导致弗莱维赫牛脂肪产量增加7.5至14.8千克，德国荷斯坦牛增加7.6至10.7千克。然而，对于蛋白质产量，主要观察到弗莱维赫牛的负面影响为-3.6至0.2千克，德国荷斯坦牛为-4.8至-5.2千克。在分析中忽略DGAT1效应时，产奶量与含量性状残差之间的皮尔逊相关性降低，从而表明DGAT1导致这些性状之间的负相关。分子检测允许在变体之间进行直接选择；然而，替代等位基因的益处取决于育种目标中赋予不同产奶性状的经济权重。
