杂种优势遗传机理的研究进展

杂种优势是生物界的一种普遍现象,对杂种优势机理的研究已将近一个世纪了,在此期间,人们提出了各种各样的假说,但杂种优势的遗传机理一直未能得到很好的解决。随着分子标记的出现和运用,杂种优势遗传机理的研究获得了新的生机。作者综述有关杂种优势产生的部分理论假说和分子机理研究。     

杂种优势的应用及基因表达的特点

杂种优势在动植物育种中得到广泛应用,然而对杂种优势分子遗传机理的研究还处在初级阶段。随着生物信息学的不断发展,对其基因表达数量和表达模式的研究也就越来越多,因为父母本的不同,杂交子代的基因在数量和功能上都存在明显差异;杂交子代融合基因的表达会发生父母本的偏向性,继而影响其表型;杂交子代中因为父母本印记的差异,导致其性状和功能有所不同。总结了杂交子代中差异基因、融合基因和印记基因的表达情况,为深入理解杂种优势的分子遗传机理提供新的切入点。     

DNA标记与动物杂种优势的关系研究进展

传统的杂种优势预测方法和杂种优势理论的缺陷限制了杂种优势的进一步利用。分子标记为杂种优势的预测和理论发展开辟了新领域。本文论述了分子标记的种类和影响分子标记预测杂种优势的因素及其在动物杂种优势研究中的应用。     

大梅与大白猪背最长肌正反消减文库的构建

杂种与亲本间的基因差异表达与杂种优势有关.为从基因差异表达的角度来研究杂种优势的机理,构建了大梅与大白猪背最长肌正反消减文库,以G3PDH为指标检测的2个文库的消减效率均达到了25倍;并从相应文库中分别挑选了550,535个有效阳性克隆,PCR检测插入片段主要分布在200～1 000 bp之间.亲本与子代肌肉组织间消减cDNA文库的构建为进一步分离、鉴定与杂种优势相关的基因,研究杂种优势的分子机理奠定了基础.     

杂种优势与分子标记关系的研究

大量存在的分子标记及其丰富的遗传变异，可以应用于辅助鉴定杂交亲本的选择以及杂种优势的预测。笔者对DNA分子标记中的一种RAPD技术以及关于杂种优势与杂种优势的预测方面作了综述。     

牧草杂种优势的研究进展

本文综述了牧草杂种优势的遗传机理、杂种优势的预测方法以及杂种优势利用等方面的研究进展,并在此基础上对牧草杂种优势今后的研究进行了展望。     

分子生物技术应用于杂种优势预测的研究进展

杂种优势预测的研究已经深入到了分子水平.作者在对杂种优势的基本理论进行阐述的基础上,着重对分子生物技术预测杂种优势的研究进行综述,并提出进一步研究的新思路.     

动物杂种优势遗传机制的研究进展

动物的杂种优势是一个早已为人类所认识的非常重要的生物学现象，由于其形成的机制比较复杂而一直都是遗传学家们研究的重点。从上个世纪初到现在已经提出了很多的假说和理论，其中的一些也在实践中得到了部分地证实，但这还远远不够，其遗传机制仍是一个亟待解决的谜。随着现代分子生物学技术的发展．我们似乎找到了破解谜底的钥匙。基于此，本文对目前已提出的形成杂种优势的遗传机制进行了回顾，希望能够更加深入的，特别是从分子水平对杂种优势的遗传机制有所认识。     

畜禽杂种优势估测方法的研究进展

本文在畜禽杂种优势理论基础上，从遗传距离法、线粒体混合试验法、蛋白质分子多态性、群间方差与群内方差之比法及分子标记法等方面综述了畜禽杂种优势估测方法的研究进展，并客观的分析了各方法的优缺点。     

畜禽杂种优势理论基础及预测的研究进展

近年来,随着分子生物学的迅猛发展,人们开始从分子水平上探讨杂种优势基因的作用和表达,进而阐明杂种优势产生的遗传基础,并在此基础上,试图提出准确可靠的杂种优势预测方法和利用途径。本文着重论述了畜禽杂种优势理论基础及预测方法研究的现状及进展,并对今后深入开展杂种优势研究提出了自己的意见和建议。     

三个鸡品系的遗传差异与杂种优势关系的研究

采用RAPD标记分析了武定鸡快羽系、绿壳蛋系和合成系间的遗传差异,进行了三个鸡品系间的杂交试验,并应用简单的线性相关分析了遗传距离指数与杂种优势的关系。分析结果表明快羽系与绿壳蛋系间的遗传差异较小,而快羽系与合成系间的遗传差异较大。品系间遗传距离指数与F1代各性状观察值均为正相关,但相关不显著;与杂种优势率之间也均为正相关,但只与13周龄存活率、种蛋受精率有显著的相关关系。表明RAPD标记在预测杂种优势上具有一定参考价值。     

畜禽杂种优势测定和评估方法的进展

现代畜牧业生产中,利用杂种优势可降低生产成本,挖掘种质资源的内在潜力,提高经济效益。在一些畜牧业发达的国家,肉用仔鸡几乎全是杂种。正是由于杂种优势在畜禽生产上的大规模应用,杂种优势的研究一直受到高度重视。作者在畜禽杂种优势理论基础上,从遗传距离法、线粒体混合试验法、蛋白质分子多态性、群间方差与群内方差之比法及分子标记法等方面综述了畜禽杂种优势测定和评估方法的研究进展,并简要、客观的分析了各方法的优缺点。     

肉牛杂交亲本遗传距离与杂种优势的相关性研究

利用11个微卫星标记研究川南山地黄牛、海福特牛、黑安格斯牛、红安格斯牛、利木赞牛、西门塔尔牛、德国黄牛的遗传多样性,分析肉牛亲本间微卫星标记遗传距离与体尺、体重杂种优势间的相关性。结果表明:11个微卫星基因座平均有效等位基因数为4.5422,7个牛种的多态信息含量在0.3434~0.4207,平均杂合度为0.6868~0.8413,7个牛种均具有丰富的多态性。亲本间遗传距离与体尺、体重杂种优势间相关系数偏小(-0.003~0.304),均未达到显著水平,用微卫星标记遗传距离预测肉牛体尺、体重杂种优势还有待进一步探讨。     

Selection for heterosis from crossbred populations: estimation of the F1 heterosis and its mode of inheritance

The heterosis inheritance backcross evaluation technique (HI-BET) is proposed as a selection strategy for developing a pair of complementary strains from a crossbred population descended from a F1 population possessing considerable heterosis. These complementary strains are expected to produce a strain cross superior to the F1 population from which they were derived. In the first stage of an experimental evaluation of HI-BET, Australorp and White Leghorn hens were compared with their F1, F2 and F1 by parental breed backcross populations for a range of egg production traits. The substantial heterosis for survivors' egg production and total egg mass was largely lost in the F2 and backcross populations indicating that this heterosis was mainly due to parental epistasis. The uneven distribution of residual heterosis in the backcross populations suggests that about two-thirds of this parental epistasis was inherited from the White Leghorn line. As the Australorp line was substantially superior to the White Leghorn line for survivors' egg production and total egg mass, it most likely contained additive genes for both these traits that were not present in the White Leghorn line. It is suggested that HI-BET should be an effective strategy for incorporating these additive genes into the White Leghorn line, together with some brown egg shell genes if also desired, as a means of further improving the performance of the F1 cross.     

Changes in heterosis under within-line selection or reciprocal recurrent selection: an experiment on early egg production in Japanese quail

In much animal production, commercial animals are crossbreds from closed lines or breeds under long-term directional selection. Therefore it is desirable to be able to predict heterosis gains over the generations as it is done for genetic progress under within-line selection. However, heterosis is the phenotypic expression of a complex phenomenon which may involve several types of genetic effects like dominance and epistasis. In animal breeding, basic quantitative genetics theory indicates that heterosis should be proportional to (squared) differences in gene frequency between populations (e.g. F alconer and M ac K ay 1996), and it has been found approximately correct, so it is commonly used for planning crosses. Under that type of heterosis, however, selection towards the same objective in two populations should bring gene frequencies closer, and therefore it should eventually decrease heterosis. On the other hand, reciprocal recurrent selection designed to increase genetic distance between lines should eventually achieve maximum heterosis (O llivier 1982). Some experiments reviewed by brun (1982) have already compared genetic progress under within-line and reciprocal recurrent selection, but they did not focus on comparing the trend of heterosis with generations between the two selection methods. Also, heterosis was monitored periodically in some selection experiments on poultry, and results were reviewed by F airfull (1990). They were somewhat contradictory, but they generally failed to relate genetic progress to loss of heterosis under within-line selection. Moreover, in commercial production, as purebreds and crossbreds are not contemporaries and are generally maintained under very different management systems, estimations of heterosis and of the evolution of crossbred advantage over the generations may be difficult to obtain. Using the Japanese quail as an experimental animal, the present work was initiated specifically to follow the changes in heterosis brought about by selection for a single heterotic trait, early egg production (M invielle et al. 1995). For that purpose, two selection methods expected to have opposite effects on heterosis, directional within-line (or individual) selection and reciprocal recurrent selection, were applied for 13 generations in four quail lines started from two different origins, and trends of heterosis in the selected character and in weight and egg traits were evaluated.     

紫花苜蓿产量育种遗传基础研究进展

就紫花苜蓿产量育种遗传基础研究进展进行了论述,并总结了紫花苜蓿在产量构成、遗传特性、杂种优势、分子标记辅助育种和QTLs定位五个方面的研究现状.     

The crossbred sire: experimental results for sheep

Crossbreeding of sheep is practiced to exploit simultaneously the use of additive and nonadditive genetic effects. The goal is to achieve optimal levels of performance appropriate for defined systems of sheep production and marketing. Although the beneficial effects of individual and maternal heterosis on sheep production have been well documented and widely implemented, considerably less is known about the effects of paternal heterosis. Limited evidence suggests that crossbred rams are more sexually aggressive and exhibit greater testicular growth than do purebred rams. Average estimates of paternal heterosis effects were 1.4, -.7 and 2.3% for seasonal fertility, prolificacy and preweaning survival, respectively. The average effect of paternal heterosis on fertility during spring breeding was 29.5%. Progeny of crossbred and purebred sires were similar in birth weight, weaning weight and postweaning growth rate and in phenotypic variation for these growth traits. However, favorable paternal heterosis effects need not exist to warrant the use of crossbred sires. Composite or F1 sires can be used as an effective method to manage the composition of additive breed effects. For example, varying proportions of germ plasm from highly prolific breeds such as the Finnsheep and Romanov can be realized through the use of crossbred sires to set reproductive rates at desired levels. Crossbred sires may be used to a greater extent to optimize additive breed effects than to exploit effects of paternal heterosis. The role of composite breeds in managing both additive and nonadditive effects is discussed.     

Inbreeding and heterosis effects on quantitative traits in a White Leghorn population under long-term reciprocal recurrent selection

1. Inbreeding and heterosis effects for quantitative traits were estimated in two White Leghorn lines selected with reciprocal recurrent selection (RRS) since 1950. 2. Pedigreed progeny were produced from full-sib, half-sib and unrelated pure line as well as reciprocal cross line matings to estimate inbreeding and heterosis effects "within sires". 3. Inbreeding effects estimated as linear regressions agreed well with estimates considering inbreeding as fixed effect. The inbreeding depression per 10% inbreeding was highest for hatchability (6-7%), intermediate for production-related traits (3%), and about 1% for shell quality, body weight and egg weight. 4. Heterosis effects were estimated by comparing pure line and cross line progeny of the same sires. 5. Results indicate considerably less heterosis for egg production than found earlier, which is interpreted as a consequence of pure line selection.