长期人工选择对群体遗传结构的影响——一项计算机模拟研究 Ⅱ.长期选择对群体遗传方差的作用

本文给出了显性与超显性模型下加性方差的分剖公式,为研究选择作用下基因间关系的变化提供了有力的方法。并模拟研究了群体大小、连锁强度与遗传力水平对遗传方差变化的影响。小群体中遗传方差在世代间波动很大;大群体中则稳定下降、波动较小。选择作用下平衡加性方差下降很快,特别是高遗传力性状。紧密连锁在小群体中一方面降低选择反应,一方面维持了更多的加性方差,从而使得预测长期选择反应甚为困难。     

氮素水平对籼、粳稻主要数量性状遗传力的影响

本文在0、35、75、105公斤/公顷4个纯氮水平下,考察了籼、粳稻各10个品种株高、结实率等12个主要数量性状遗传力的变化规律。结果表明,性状不同,其遗传力受氮素的影响程度也不同,两亚种皆然,但籼稻的遗传力均比粳稻的高,籼稻群体比粳稻群体更具遗传多样性。因此,育种实践中,应将目标性状设在最宜于其遗传信息充分表达的氮素水平下进行选择。     

高粱主要性状遗传力和相关性的初步研究

任何一种性状的表现型都是其内部的遗传型和外部的环境条件共同作用的结果,所以性状的表现型变量可分解为遗传变量和环境变量两部分。遗传力就是遗传变量与表型变量(总变量)的比率,遗传力比率越高表明性状的遗传变量在表现型变量中占的成分越大,是高度遗传的,因而选择也越有效。因此估算遗传力可以确定系统选择的指标和杂种的选择世代及原始材料的利用价值。遗传相关是估算性状间的遗传型相关程度,在育种中可根据性状的表现型相关程度,从一个性状间接地选择另一个性状。     

氮素水平对釉、粳稻主要数量性状遗传力的影响

本文在0、35、75、105公斤／公顷4个纯氮水平下,考察了仙、粳稻各10个品种株高、结实率等12个主要数量性状遗传力的变化规律。结果表明,性状不同,其遗传力受氮素的影响程度也不同,两亚种皆然,但釉稻的遗传力均比粳稻的高,釉稻群体比粳稻群体更具遗传多样性。因此,育种实践中,应将目标性状设在最宜于其遗传信息充分表达的氮素水平下进行选择。     

大豆不同亲本类型F2主要性状遗传参数分析

对大豆3个不同亲本类型的杂交组合F2群体主要性状遗传变异系数、遗传力和遗传进度进行了估算分析,结果表明这些遗传参数因性状或亲本类型的不同而有明显差异.含有野生亲缘关系的组合,类型间、性状间F2遗传力有较大差异,性状变异幅度增大,相对遗传进度也较大,从而有较广泛的选择基础.     

大豆不同亲本类型F2主要性状遗传参数分析

对大豆3个不同亲本类型的杂交组合F2群体主要性状遗传变异系数、遗传力和遗传进度进行了估算分析,结果表明：这些遗传参数因性状或亲本类型的不同而有明显差异。含有野生亲缘关系的组合,类型间、性状间F2遗传力有较大差异,性状变异幅度增大,相对遗传进度也较大,从而有较广泛的选择基础。     

长期指数选择的遗传效果分析—计算机模拟研究

本文利用Monte Carlo模拟技术研究比较了普通选择指数、实际选择指数、约束指数和单性状选择四种方法的长期选择效果及对群体遗传结构的影响。50世代的结果表明:群体大小和遗传参数能明显影响长期指数选择的反应;实际指数选择是有效的,其总体效果好于普通指数;约束选择的早期反应虽低于普通指数,但后期效果好,而且对群体遗传结构影响较小。同时,指数选择使性状加性遗传方差和遗传力衰减变化,而遗传相关依指数公式的系数呈定向改变。建议多性状长期选择时应用实际指数法或约束指数法。     

性状遗传力与QTL方差对标记辅助选择效果的影响

在采用动物模型标记辅助最佳线性无偏预测方法对个体育种值进行估计的基础上,模拟了在一个闭锁群体内连续对单个性状选择10个世代的情形,并系统地比较了性状遗传力和QTL方差对标记辅助选择所获得的遗传进展、QTL增效基因频率和群体近交系数变化的影响。结果表明：在对高遗传力和QTL方差较小的性状实施标记辅助选择时,可望获得更大的遗传进展;遗传力越高,QTL方差越大,则QTL增效基因频率的上升速度越快;遗传力较高时,群体近交系数上升的速度较为缓慢,而QTL方差对群体近交系数上升速度的影响则不甚明显。结合前人关于标记辅助选择相对效率的研究结果,可以认为：当选择性状的遗传力和QTL方差为中等水平时,标记辅助选择可望获得理想的效果。     

夏谷主要性状遗传力、遗传相关和选择指数的初步研究

夏谷性状的遗传力以码数为最高,株高和千粒重次之,以单株产量和株穗重最低,而小区产量的遗传力(集团群体的诸性状的综合表现)却更高。因此在选种上采用产量对比选拔高产优系要比选择高产单株的效果为好。遗传相关可以排除环境的干扰,做为选择的依据决定取舍较为可靠。可以从选择遗传力最高的性状入手,间接地选择出遗传力较低的主要经济性状。选择指数公式中的权数,因性状组合的不同而异,据此产生的选择效果也不同,应该选用比直接选择具有更高效率的选择指数,以判别选择对象的优劣。     

大麦杂种F2群体主要农艺性状遗传力和遗传进度的初步研究

大麦的主要农艺性状大都属于数量性状, 受微效多基因控制,易受环境条件的影响,在杂 种分离世代中,个体性状呈现连续分布,这给正 确地配组和有效地选择带来了一定的困难。运 用数量遗传研究方法对大麦农艺性状的遗传力 和遗传进度进行估测,可以衡量遗传和环境影 响对于表型总变异的相对重要性及在一定选择 压力下的选择效果,可为杂种后代的选择和处 理提供参考依据。国外对大麦的研究甚多,而 国内较少。我们试图通过大麦杂种Fz群体主 要农艺性状的遗传力和遗传进度的初步研究, 为大麦育种提供一些依据。     

Recent advances in the study of Kaposi's sarcoma-associated herpesvirus replication and pathogenesis

It has now been over twenty years since a novel herpesviral genome was identified in Kaposi's sarcoma biopsies. Since then, the cumulative research effort by molecular biologists, virologists, clinicians, and epidemiologists alike has led to the extensive characterization of this tumor virus, Kaposi's sarcoma-associated herpesvirus(KSHV; also known as human herpesvirus 8(HHV-8)), and its associated diseases. Here we review the current knowledge of KSHV biology and pathogenesis, with a particular emphasis on new and exciting advances in the field of epigenetics. We also discuss the development and practicality of various cell culture and animal model systems to study KSHV replication and pathogenesis.     

The structure, reproduction and taxonomy of Vidalia and Osmundaria (Rhodophyta, Rhodomelaceae)

Comprises species occurring mostly in subtidal habitats in tropical, subtropical and warm-temperate areas of the world. An analysis of the type species, V. spiralis (Sonder) Lamouroux ex J. Agardh, a species from Australia, establishes basic characters for distinguishing species in the genus. These characters are (1) branching patterns of thalli, (2) flat blades that may be spiralled on their axis, (3) width of the blade, (4) primary or secondary derivation of sterile and fertile branchlets and (5) position of sterile and fertile branchlets on the thalli. Application of the latter two characters provides an important basic method for separation of species into three major groups. Osmundaria , a genus known only in southern Australia, was studied in relation to Vidalia , and its separation from the Vidalia assemblage is not accepted. Species of Vidalia therefore are transferred to the older genus name, Osmundaria. Two new species, Osmundaria papenfussii and Osmundaria oliveae are described from Natal. Confusion in the usage of the epithet, Vidalia fimbriala Brown ex Turner has been clarified, and Vidalia gregaria Falkenberg, described as an epiphyte on Osmundaria pro/ifera Lamouroux, is revealed to be young branches of the host, Osmundaria prolifera.     

New or rare chromosome counts in Artemisia L. (Asteraceae, Anthemideae) and related genera from Kazakhstan

Fifteen chromosome counts of six Artemisia taxa and one species of each of the genera Brachanthemum, Hippolytia, Kaschgaria, Lepidolopsis and Turaniphytum are reported from Kazakhstan. Three of them are new reports, two are not consistent with previous counts and the remainder are confirmations of very scarce (one to four) earlier records. All the populations studied have the same basic chromosome number, x = 9, with ploidy levels ranging from 2x to 6x. Some correlations between ploidy level, morphological characters and distribution are noted.     

肝癌中HBV和HCV基因和抗原的分布及意义

采用原位分子杂交方法检测HCV RNA及HBV X基因;采用免疫组织化学方法研究HCV核心抗原,非结构区C33c抗原及HBxAg在肝细胞肝癌中的定位及分布.结果表明(1)HCV RNA、HBV X基因在肝细胞肝癌组织检出率分别为40%(55/136)和82%(112/136).HCV RNA定位于癌细胞的胞浆内,阳性细胞呈散在、灶状及弥漫分布三种形式;HBV X基因在肝癌细胞中的分布呈胞浆型、核型及核浆型,阳性细胞也呈上述三种分布形式;(2)HCV C33c抗原、核心抗原在肝细胞肝癌中的阳性率为81%(133/164)及86%(141/164).C33c抗原定位于癌细胞及肝细胞的胞浆内;核心抗原既定位于癌细胞核中,又可定位于胞浆中.C33c抗原阳性细胞以灶状分布为主;而核心抗原阳性细     

Selection with two alleles and complete dominance

For a plant selection model with frequency-independent viabilities, fertilities and selfing rates, it is shown that apart from global fixation, for certain parameter combinations a protected polymorphism and facultative fixation (either allele may become fixed according to initial frequencies) may both occur. Facultative fixation requires different selling rates for the dominant and recessive type. Protection of the polymorphism requires resource allocation for male and female function. In this connection the problem of purely genetically caused population extinction is discussed.
For general frequency dependence and regular segregation, the chances for establishment of a completely recessive gene are compared to those of a completely dominant gene. It is proven that the process of establishment of the recessive gene, despite a fitness advantage, may be considerably endangered by drift effects if random mating prevails. The recessive gene may reach the same effectivity in establishment as a dominant gene, only if the recessive homozygote mates exclusively with its own type during the period of establishment.