杂种优势遗传学基础的研究进展

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近一个世纪但仍未能解决，随着分子标记的出现及应用，杂种优势遗传机理研究获得了新的生机。本文综述杂种优势产生的基因理论假说以及分子机理研究。     

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。     

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。     

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。     

肉兔生产中的杂种优势

杂种优势利用是加快肉兔遗传改良的有效途径,在肉兔育种中被广泛应用。但目前对杂种优势产生的相关遗传机理认识不足。亲本间的遗传差异与杂种优势关系密切。概述了杂种优势的相关遗传机理和部分肉兔杂种优势的测定结果,为合理利用杂种优势进行肉兔生产提供理论依据。     

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。     

应用DNA指纹技术研究湖北白猪的杂种优势

本研究利用ＤＮＡ指纹技术，通过人源小卫星探针３３６分析湖北白猪Ⅲ系、Ⅳ系，长白与杜洛克的遗传纯度与遗传距离，通过分析遗传距离与杂交组合试验资料表明，湖北白猪Ⅲ系（或Ⅳ系）与杂交品种间遗传距离大时，杂交组合的日增重、饲料转化率、瘦肉率、繁殖性状的杂种优势大；反之，遗传距离小时，其主要性状的杂种优势相应较小，根据杂交组合间的遗传距离可以预测杂交组合的杂种优势。     

猪若干经济性状的杂种优势与遗传方式探讨

杂交效果的好坏,既取决于双亲的遗传纯度,又取决于双亲的遗传距离,还取决于性状的遗传方式。据外国学者报道,猪的繁殖力、生活力等遗传力低的性状,杂种优势明显,呈显性遗传,背膘厚与胴体性状属高遗传力的性状,杂种优势不明显,呈中间遗传。而国内学者报道,猪的某些胴体性状有较强的杂种优势,呈显性或超显性遗传。为进一步探讨猪的若干数量性状的杂种优势与遗传方式,作者利用“以湖北白猪Ⅳ系为母本的杂交组合试验”材料,计算了不同杂交组合各类性状的杂种优势率,并对这些性状的遗传方式进行了初步研究。     

家蚕数量性状遗传距离的研究初报

应用多元统计分析方法,估算了15个家蚕品种数量性状的遗传距离,并用遗传距离作聚类分析,计算了十项数量性状的杂种优势率与遗传距离的相关性。初步认为:(1)应用遗传距离进行聚类分析,在类群间选配杂交组合具有一定的实用意义;(2)遗传距离与全茧量、万蚕产茧量、茧层量、万蚕产茧层量、虫蛹率的杂种优势有高度的正相关,与茧丝长、茧丝量的杂种优势率也呈显著的正相关,而与茧层率、茧丝纤度、净度的杂种优势率几乎没有相关关系;(3)遗传距离可以作为预测某些数量性状杂种优势的一个参数。     

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。     

动物杂种优势利用及其预测方法

杂种优势因具有提高两个不同亲本的遗传组成杂交所产后代的生产性能、生活力和抗逆性等特点,被广泛地运用在动植物杂交育种中。杂种优势利用率越高,种畜产生的价值越高,其后代产生的额外利润就越大。因此,杂种优势的利用率是广大育种工作者所关注的一项重要内容。杂种优势利用率的评估则依赖于对种畜杂种优势大小的预测。本文主要从杂种优势利用和杂种优势预测方法2个方面对已有的研究进行综述,并探讨有关杂种优势预测准确度提高的方法,以期对相关的研究提供一定的参考和帮助。     

家畜杂种优势估测方法研究进展

本文论述了有关家畜杂种优势,特别是母本杂种优势、父本杂种优势以及重组效应的估测原理与方法的最新进展。介绍了11个有关估计杂种优势的公式,并说明了这些公式的使用条件。     

多环境条件下家蚕主要经济性状杂种优势表现

分析了家蚕15个经济性状在不同年份和季节饲养的5次试验的杂种优势表现.得出:在不同的环境条件下,家蚕经济性状的杂种优势率的均值和均方均存在着明显的差异,因而可以把家蚕的经济性状根据其杂种优势的表现不同分成几类,文章讨论了各类性状对组配杂交组合的影响.     

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.     

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。     

野牛草杂交子代坪用性状观测及其杂种优势测定

以4个母本、4个父本共8个亲本为材料,采用不完全双列杂交试验设计,测定了杂交亲本及其子代叶片颜色、枯黄程度及二者的杂种优势.研究发现不同杂交组合的枯黄程度杂种优势不大,但各组合间的叶片颜色的杂种优势差异较大,同一亲本在不同组合中的杂种优势值不同.     

苜蓿雄性不育系杂交组配组合光合生理特性及杂种遗传力研究

通过对苜蓿（Medicago sativa）雄性不育系及其杂交组合的光合生理特性和杂种遗传力测定,以及与杂种优势间的相关性分析,结果表明：杂交组合净光合速率（Pn）和蒸腾速率（Tr）日变化均呈现“单峰”曲线。在消耗等量的水分条件时,合成的自身干物质较多,即水分利用效率（WUE）高则其杂种优势明显。表明水分利用效率是杂种优势形成的主要光合生理指标,而蒸腾速率对产量性状杂种优势形成影响不大;杂交组合的杂种遗传力值的变异范围均在0~1之间,其中杂交组合2×Ⅱ的杂种遗传力最高（0.6129）,同时其杂种优势效应值也最高（52.10%）;杂交组合的杂种遗传力与杂种优势效应间存在极显著正相关,因此杂种遗传力可对杂种优势效应有直接影响。     

Breed effects and heterosis in advanced generations of composite populations for preweaning traits of beef cattle

The effects of heterosis for gestation length, dystocia, calf survival, birth weight, 200-d weight, and ADG from birth to weaning were evaluated in F1, F2, and combined F3 and F4 generations in three composite populations. Breed effects were evaluated for the nine parental breeds (Red Poll, Hereford, Angus, Limousin, Braunvieh, Pinzgauer, Gelbvieh, Simmental, and Charolais) that contributed to the three composite populations. Breed effects were significant for all traits evaluated except survival at birth. The large differences among breeds in additive direct and additive maternal genetic effects offer a great opportunity to use the genetic differences among breeds to achieve and maintain optimum additive genetic (breed) composition to match genetic resources to a wide range of production-marketing ecosystems. There was no heterosis for gestation length. Mean heterosis for dystocia was significant estimated in F1 but not in F2 or in the combined F3 and F4 generations. Mean heterosis was not significant in any generation for survival at birth, to 72 h, and to weaning for the F1 generation; mean heterosis was significant for survival to weaning for the F2 generation and approached significance (P = .06) for the combined F3 and F4 generations. Mean heterosis over all composite populations and heterosis for each composite population were significant in all generations for weight at birth and at 200 d and for ADG from birth to weaning. Retained heterosis was not less than expected from retained heterozygosity in composite populations for the traits evaluated. These results suggest that heterosis for these traits likely is due to dominance effects and, thus, can be attributed to the recovery of accumulated inbreeding depression in the parental breeds.     

三元杂交多性状综合杂种优势测定方法的改进

本文应用主成分分析原理提出测定三元杂交多性状综合杂种优势的改进方法，将多性状综合杂种优势定义为各主成分杂种优势与其相对重要权乘积和。此法消除了性状间相关和环境因素的影响，所获得的综合杂种优势估计值合理可靠。本文所提出的方法也可用于测定其它类型杂交试验多性状综合杂种优势。