分子遗传标记在奶牛标记辅助选择中的应用

分子标记是目前研究比较多的一类遗传标记,遗传标记主要包括有形态学标记、细胞学标记、生化标记和分子标记等.前3种是基因表达的结果,是对基因差异的间接反映,易受环境和其他因素的影响.而分子标记直接从DNA分子水平上反映差异,不受环境、发育阶段、组织等的影响,稳定可靠,多态性好,因而在家畜育种中被广泛利用,特别是在标记辅助选择中.标记辅助选择利用分子标记与QTL之间的连锁不平衡,通过对分子标记的选择来实现对QTL的选择达到家畜育种目的.     

分子标记在动物抗病育种中的研究进展

综述了利用分子标记寻找抗性 /易感性基因、与抗性 /易感性相关候选基因和定位抗性 /易感性 QTL以及特定分子标记与它们的紧密连锁关系的国内外研究动态 ,从而进行标记辅助选择 ( MAS)抗病育种。     

动物遗传标记辅助选择研究进展

随着分子遗传学、分子生物技术、数量遗传学和计算机技术的飞速发展,有关分子遗传标记和标记辅助选择方面的研究广泛地开展起来。一种新的选种方法—标记辅助选择(marker-assistedselection,MAS)在家畜育种中产生了巨大的影响,尤其是大量的分子遗传标记和数量性状座位(QTL)图谱     

遗传标记在四川黑山羊研究中的应用

综述了遗传标记中的生物化学标记和分子标记在四川黑山羊遗传育种中的应用,重点论述了分子标记随机扩增多态DNA、DNA指纹、随机片段长度多态、微卫星DNA、线粒体DNA在四川黑山羊的起源和进化、群体亲缘关系及群体遗传结构分析、重要经济性状标记、基因图谱的构建和QTL定位、标记辅助选择(MAS)、系谱鉴定与亲子鉴定,以及杂种优势预测等方面的应用。并对其发展前景作了展望。     

利用玉米骨干系进行产量及相关性状的QTL分析

玉米重要性状QTL定位是分子标记辅助选择的前提条件,对于提高育种效率有重要意义。本研究以当前大面积推广的一个优良玉米杂交种郑单958的两个亲本(郑58x昌7.2)构建含有225个家系的F2:3群体为基础材料,构建了SSR分子标记遗传连锁图谱,并对产量和相关性状进行了QTL作图。     

分子标记及其在标记辅助选择中的应用

运用分子标记来进行标记辅助选择,已经成为当今家畜育种的一种趋势。笔者对目前常见的几种分子标记进行了简要介绍,并就分子标记在标记辅助选择中的应用,特别就分子标记在标记辅助选择中分子标记图谱的构建、分子标记的筛选、QTL定位和与分子标记的连锁分析3个方面的应用作了较详尽的综述。     

分子遗传标记技术及其在动物育种中的研究进展

遗传标记经历了从传统的标记即形态学标记、细胞学标记、生物化学标记到现代分子标记的发展,分子标记具有很多优势,也促进了动植物育种、人类医学、基因定位以及构建遗传图谱的改革。遗传标记能应用于畜禽的遗传多样性分析、种质资源的鉴定、亲缘关系的研究、遗传图谱的构建、分子标记辅助选择和QTL定位等领域,文章主要综述了分子标记在标记辅助选择的应用。     

标记辅助选择改良猪经济性状的研究进展

标记辅助选择是近些年随着分子标记技术的发展而出现的一种新型选种方法，被认为是提高育种选择效率的一种有效方法。此文系统地综述了近年来猪重要经济性状的主效基因或数量性状座位(QTL)定位及猪标记辅助选择的应用概况、实施方法和策略等方面的研究进展，并在此基础上就当前应用分子标记辅助选择进行猪经济性状遗传改良的相关问题进行了讨论。     

家蚕主要经济性状的QTL定位研究进展

家蚕经济性状改良一直是蚕育种工作者的重要目标之一,随着分子生物学技术的发展,控制家蚕经济性状的数量性状位点(QTL)定位研究工作得以大量开展,使得家蚕分子标记辅助育种成为可能。综述了家蚕遗传图谱的构建进程、家蚕QTL定位常用分离群体、茧质性状QTL定位研究现状,并分析了家蚕经济性状QTL定位研究中存在的问题,以期为推进家蚕分子标记辅助育种提供参考。     

猪育种的经济性状选择与生产性能测定

1育种技术的发展随着数量遗传学理论的发展,育种学家可以借助一定的统计学方法将性状的表型值进行剖分,并从中估计出可以真实遗传的部分,即育种值,使畜禽育种由表型值选择发展为育种值选择,从而提高了选种的准确性和效率。随着分子生物学技术突飞猛进的发展,对分子遗传标记、QTL图谱分析的研究正不断深入。目前,畜禽遗传图谱的构建已取得了较大的进展,使得利用1个或1群标记以区分不同个体QTL的有利基因型正在逐步成为现实。标记辅助选择就     

标记辅助选择在猪育种中应用效果的研究

本研究针对猪育种中重点考虑的窝产活仔猪数（NBA）、达100 kg体重日增重（ADG）、饲料利用率（FCR）、达100 kg体重的背膘厚（BF）、肌内脂肪含量（IMF） 5个性状,利用连锁平衡（linkage equilibrium,LE）、连锁不平衡（linkage disequilibrium,LD）标记和直接标记（direct marker,DR）3种类型的分子遗传标记,设计了3个规模不同的基础群,母猪数分别为100、200、300头,公猪数都为10头,基础群个体间无亲缘关系,育种群实施闭锁繁育。用Monte Carlo方法模拟了MAS的5个世代选择试验。育种值估计采用标准BLUP（Standard BLUP,SBLUP）模型（此育种值作为对照）、QBLUP模型（使用DR标记）、MBLUP模型（使用LD和LE标记）。结果表明,利用DR标记在各种情况下都比利用LD和LE标记获得的选择效率高;5个性状中,MAS对低遗传力、限性性状NBA的选择效率最高;当性状的QTL方差占遗传方差基本相同时,中等遗传力性状FCR的选择效率比高遗传力性状BF的更高;当性状的遗传力差异不大时,QTL方差占遗传方差比例大的性状FCR的选择效率比QTL方差占遗传方差比例小的性状ADG的更高。当利用QBLUP模型时,MAS对NBA的选择效率最高,ADG的选择效率最低。     

Linkage disequilibrium and selection response in two-stage marker-assisted selection of dairy cattle over several generations

A stochastic simulation was carried out to investigate the advantage of marker‐assisted selection (MAS) in comparison with traditional selection over several generations. The selection goal was a sex‐limited trait or a linear combination of traits with a polygenic component, two unlinked additive QTL and a non‐genetic component. The simulated QTL were moderate or large and the allele frequencies were varied. Two stages of selection among the male offspring were carried out. In the first stage marker information was used to select among full sibs (MAS) or one full sib was chosen at random. In the second stage young bulls were selected based on a progeny test. The response in total genetic gain was faster with MAS than with traditional selection and persisted over several generations. With a QTL of moderate size and initial allele frequencies of the favourable allele of 0.05 the response with MAS was 6% higher than with traditional selection in the sires selected after progeny test. MAS in a within‐family two‐stage selection scheme improved the genetic merit of selected bulls even when linkage disequilibrium between QTL and polygenes was initially increased.     

Marker‐assisted selection reduces expected inbreeding but can result in large effects of hitchhiking

We used computer simulations to investigate to what extent true inbreeding, i.e. identity‐by‐descent, is affected by the use of marker‐assisted selection (MAS) relative to traditional best linear unbiased predictions (BLUP) selection. The effect was studied by varying the heritability (h² = 0.04 vs. 0.25), the marker distance (MAS vs. selection on the gene, GAS), the favourable QTL allele effect (α = 0.118 vs. 0.236) and the initial frequency of the favourable QTL allele (p = 0.01 vs. 0.1) in a population resembling the breeding nucleus of a dairy cattle population. The simulated genome consisted of two chromosomes of 100 cM each in addition to a polygenic component. On chromosome 1, a biallelic QTL as well as 4 markers were simulated in linkage disequilibrium. Chromosome 2 was selectively neutral. The results showed that, while reducing pedigree estimated inbreeding, MAS and GAS did not always reduce true inbreeding at the QTL relative to BLUP. MAS and GAS differs from BLUP by increasing the weight on Mendelian sampling terms and thereby lowering inbreeding, while increasing the fixation rate of the favourable QTL allele and thereby increasing inbreeding. The total outcome in terms of inbreeding at the QTL depends on the balance between these two effects. In addition, as a result of hitchhiking, MAS results in extra inbreeding in the region surrounding QTL, which could affect the overall genomic inbreeding.     

Theoretical efficiency of multiple-trait quantitative trait loci-assisted selection

The effectiveness of five selection methods for genetic improvement of net merit comprising trait 1 of low heritability (h² = 0.1) and trait 2 of high heritability (h² = 0.4) was examined: (i) two‐trait quantitative trait loci (QTL)‐assisted selection; (ii) partial QTL‐assisted selection based on trait 1; (iii) partial QTL‐assisted selection based on trait 2; (iv) QTL‐only selection; and (v) conventional selection index without QTL information. These selection methods were compared under 72 scenarios with different combinations of the relative economic weights, the genetic correlations between traits, the ratio of QTL variance to total genetic variance of the trait, and the ratio of genetic variances between traits. The results suggest that the detection of QTL for multiple‐trait QTL‐assisted selection is more important when the index traits are negatively correlated than when they are positively correlated. In contrast to literature reports that single‐trait marker‐assisted selection (MAS) is the most efficient for low heritability traits, this study found that the identified QTL of the low heritability trait contributed negligibly to total response in net merit. This is because multiple‐trait QTL‐assisted selection is designed to maximize total net merit rather than the genetic response of the individual index trait as in the case of single‐trait MAS. Therefore, it is not economical to identify the QTL of the low heritability traits for the improvement of total net merit. The efficient, cost‐effective selection strategy is to identify the QTL of the moderate or high heritability traits of the QTL‐assisted selection index to facilitate total economic returns. Detection of the QTL of the low h² traits for the QTL‐assisted index selection is justified when the low h² traits have high negative genetic correlation with the other index traits and/or when both economic weights and genetic variances of the low h² traits are larger as compared to the other index traits of higher h². This study deals with theoretical efficiency of QTL‐assisted selection, but the same principle applies to SNP‐based genomic selection when the proportion of the genetic variance ‘explained by the identified QTLs’ in this study is replaced by ‘explained by SNPs’.     

畜禽数量性状基因座位的精细定位

数量性状基因座位(QTL)的精细定位是实施QTL克隆及标记辅助选择(MAS)的重要基础。然而就目前畜禽QTL定位的结果来看,除了通过候选基因法识别的少数基因外,大多数QTL定位的精度仍无法满足实际应用的要求。为进一步提高QTL定位的精度,缩小QTL定位的置信区间,人们相继提出并发展了一系列新的QTL定位方法。本文在分析畜禽QTL定位的基本方法及影响畜禽QTL定位精度的主要因素基础上,对提高QTL定位精确性的策略和方法进行了相应的探讨。     

传递不平衡检测及其在QTL精细定位中的应用

在早期的QTL定位研究中,研究者所关注的主要是QTL检出效率的高低。随着QTL定位研究的不断深入,研究者们发现：即使是在QTL检出效率很高的情况下,其定位的精确性仍然可能很低。就目前的定位精度来看,虽然基本可以满足实施标记辅助选择的要求,但还远远不能满足分子克隆技术所能达到的操作程度。因此有必要寻找新的定位策略以达到QTL精细定位的目的。本文简要综述了QTL精细定位新策略-传递不平衡检测（TDT）的概念及发展、原理与方法及其在QTL精细定位中的应用。     

Use of marker haplotypes to refine covariances among relatives for breeding value estimation

Markers flanking DNA regions, where quantitative trait loci (QTL) have been previously spotted, can be used to trace the common inheritance of major genes for a better definition of covariances among animals. A practical approach to the use of marker data to refine the additive relationship matrix used in the traditional best linear unbiased prediction (BLUP) methodology is presented. The technique allows the number of the mixed model equations to be kept to an animal level, blending polygenic pedigree data with marker haplotype information. The advantage of this marker-assisted selection (MAS) approach over BLUP selection has been assessed through a stochastic simulation. A finite locus model with 32 independent biallelic loci was generated with normally distributed allelic effects. The heritability of the trait, measured on both sexes and on females only, was set to 0.2 and 0.5. Five-allelic markers 2, 10 and 20 cM apart, bracketed the QTL with the largest effect on the trait, accounting for 17% of the genetic variance. The bracketed QTL had two or eight alleles and its position was undefined within the bracket. Results show a moderate 2% advantage of MAS over BLUP in terms of higher genetic response when trait was recorded on both sexes and heritability was 0.2. The benefit is in the short term, but it lasts longer with polyallelic QTL. When the trait was recorded on females only, MAS produced only a small and insignificant genetic gain, but reduced the overall inbreeding in the population. MAS was also inefficient when heritability was 0.5.     

The Research Progress of Molecular Technology for Dairy Cattle Breeding

Molecular breeding technology is direct selection at the DNA level by randomly distributed molecular markers throughout the genome polymorphism comparison,it is helpful to carry out more comprehensive study of polymorphism on investigated subjects,meanwhile,more information can be got,and the accuracy of selection will be higher,thereby,the milk production efficiency and economic benefits can be improved.From the perspective of the dairy cattle molecular breeding technology,the author expounds the research challenges,problems and research progress on several aspects,such as localization of QTL,MAS,transgenic breeding and GWAS,points out that molecular breeding techniques have a very important role in dairy cattle breeding and improvement process.Further research and application of molecular breeding technology not only can accelerate the development of dairy cows in the core group of comprehensive construction,but also is very necessary to cultivate a bull.     

奶牛分子育种技术研究进展

分子育种技术是在DNA水平上直接进行选择,通过对随机分布于整个基因组的分子标记的多态性进行比较,更加全面地了解研究对象的多态性,可以获得更大的信息量,选种的准确性也更高,进而提高奶牛生产效率和经济效益。作者从奶牛分子育种技术的角度入手,阐述了数量性状基因的定位、分子标记辅助选择、转基因育种以及全基因组关联分析这几方面的研究难点、存在问题和研究进展,指出分子育种技术在奶牛育种及改良过程中具有非常重要的作用,进一步研究并应用分子育种技术,不仅可以加速我国奶牛核心群的全面建设,而且对培育种公牛也是非常必要的手段。     

Accounting for uncertainty in QTL location in marker-assisted pre-selection of young bulls prior to progeny test

The objective of this study was to evaluate whether the efficacy of marker assisted selection (MAS) could be improved by considering a confidence interval (CI) of QTL position. Specifically, MAS was applied for within-family selection in a stochastic simulation of a closed nucleus herd. The location and effect of the QTL were estimated by least squares interval mapping with a granddaughter design and marker information was then used in a top down scheme. Three approaches were used to select the best bull within full sibships of 3 or 40 bulls. All three were based on the probability of inheriting the favorable allele from the grandsire (PROB). The first method selected the sib with the highest PROB at the location with the highest F-ratio (MAX). The other two approaches were based on sums of estimated regression coefficients weighted by PROB at each cM within a 95% CI based on either bootstrapping (BOOT) or approximate LOD scores (LOD).
Accounting for CI increased the relative genetic gain in all scenarios. The average breeding value (BV) of the selected bulls was increased by 2.00, 2.60 and 2.59% when MAS was applied using MAX, BOOT and LOD, respectively, compared to random selection (h²=0.30). Selected bulls carried the correct allele in 63.0, 68.5, 67.6 and 50.1% of the cases for MAX, BOOT, LOD and random selection, respectively.