人类遗传负荷与近亲结婚

据Mckusick统计,人类单基因病及异常性状已达6457种。染色体畸变综合症和多基因病均在IOO种左右。故人类约有1／5～1／4的人患有某种遗传病或与遗传有关的疾病。这不能不引起人们极大的关注。那么人类的遗传负荷（geneticload）到底有多大？遗传负荷是指一个群体中,由于致死基因或有害基因的存在而使该群体适合度降低的现象。遗传负荷一般用群体中每个个体平均所携带的致死基因或有害基因的数量来衡量。1人类群体遗传负荷的估计方法一个群体的遗传负荷的高低,主要决定于常染体隐性致病基因的频率。而个体患遗传病的威胁,主要来自有害…     

论替换负荷与Haldane进退维谷

在等位基因A优于等位基因α的选择下,种群中不存在有现实意义的H－W平衡;用平衡频率导出的Haldane进退维谷只是一种数学佯谬;替换负荷是选择下的非平衡种群的遗传负荷,且亲代负荷最大,随着世代的增加,后代负荷越来越小,种群对选择越来越适应。     

中国水青冈种内种间遗传多样性的初步研究

本文利用凝胶电泳法研究了亮叶水青冈(Fagus lucida)、巴山水青冈(F. pashanica)和米心水青冈(F. engleriana)的遗传多样性。所测定的酶系统包括：过氧化物酶(PX₁和PX₂)、磷酸葡萄糖脱氢酶(PGD)、超氧化物歧化酶(SOD)、谷氨酸草酰乙酸转氨酶(GOT₁和GOT₂)、异柠檬酸脱氢酶(IDH)、甲基萘醌还原酶(MNR)、葡萄糖磷酸变位酶(PGM₁和PGM₂)和苹果酸脱氢酶(MDH₂)8种酶系统,测定和分析了3种水青冈的等位基因频率和遗传距离指标,为进一步研究水青冈属各种间的亲缘关系和进化提供了科学依据。     

中国4种蝗虫不同种群的遗传分化

采用水平淀粉凝胶电泳技术,应用等位酶分析方法对采自我国山西、江苏、河北等地不同蝗区优势蝗虫种类3科4种8个种群的12种酶18个酶位点进行了检测,比较了4种蝗虫种群水平的等位基因频率变化和它们之间的遗传距离。等位基因频率分析表明：中华稻蝗和笨蝗各位点等位基因丰富,而长翅素木蝗和短额负蝗各位点等位基因较少。在所研究的4种蝗虫8个种群中,多态位点百分率普遍较高(P＝53．3％—100．0％),由于杂合子数目较少而使每个位点的平均杂合度观察值偏低(H。＝0．034—0．139)。受迁飞能力、繁殖方式和活动范围的限制,4种蝗虫的平均杂合度观察值表现出一定的差异：笨蝗较高(H。＝0．089—0．139),其次是中华稻蝗(H。＝0．073—0．090),而长翅素木蝗(H。＝0．0488—0．068)和短额负蝗(H。＝0．034—0．050)相对较低。除Adk-1、Ao-1、Idh-1、Ldh-1、Ldh-2和Me-1在部分蝗虫种群符合Hardy-Weinberg平衡外,其余绝大多数位点的基因型频率显著偏离H—W平衡,但短额负蝗的多个位点符合或接近H—W平衡,表明该种蝗虫在自然种群结构方面明显有别于其他种类。从4种蝗虫的F—统计量(Fst)看,笨蝗种群间基因分化程度最高(Fst＝0．32),其次是短额负蝗(Fst＝0．31),而中华稻蝗相对较低(Fsl＝0．20),长翅素木蝗种群间基因分化程度最低(Fsl＝0．18),利用非加权算术平均法(UPGMA)对I值和D值进行聚类,所得聚类树也证实了这种遗传分化差异,上述结果反映了迁飞能力、适应性和环境因子对不同蝗虫遗传分化的影响。Nei的遗传距离(D)和遗传一致度(I)进行的聚类分析基本符合传统形态学、细胞学等研究结果：即同属于斑腿蝗科的中华稻蝗和长翅素木蝗遗传距离最小(D＝0．559),遗传一致度最高(I＝0．576)。在3个科中,癞蝗科和锥头蝗科之间呈现较小的遗传距离(D＝0．776)和较高的遗传一致度(I＝0．776),而这两科与斑腿蝗科之间的遗传距离相对较大(D＝0．908),遗传一致度相对较低(I＝0．406)。等位酶分析能较好地反映蝗虫不同物种的亲缘关系和种内不同种群之间的遗传分化程度。     

中华稻蝗三种群遗传结构分析

应用淀粉凝胶电泳对山西省太原黄陵村、临猗县赵村及永济县伍姓湖3个中华稻稻（Oxya chinensis）种群的4个等位酶位点（MDH-1、MDH-2、LDH、ME）进行了分析。结果表明3个种群的中华稻蝗在遗传结构上具有差异;黄陵种群的MDH-1、MDH-2以及伍姓湖种群的MDH-1均为单态位点;赵村种群的杂合性最低（H=0.112）,伍姓湖种群最高（H=0.229）;赵村种群与伍姓湖种群间的Nei‘s遗传距离为0.068,可视为1个大的种群,而黄陵种群与赵村种群和伍姓湖种群的Nei‘s遗传距离分别为0.247和0.218。考虑到赵村和伍姓湖之间的地理距离（41km）比太原黄陵（357km）要近得多,结果提示3个种群地理距离与遗传结构差异之间存在相关关系。     

微生物生态学理论框架

微生物是生态系统的重要组成部分,直接或间接地参与所有的生态过程。微生物生态学是基于微生物群体的科学,利用微生物群体DNA/RNA等标志物,重点研究微生物群落构建、组成演变、多样性及其与环境的关系,在生态学理论的指导和反复模型拟合下由统计分析得出具有普遍意义的结论。其研究范围从基因尺度到全球尺度。分子生物学技术的发展,使人们可以直接从基因水平上考查其多样性,从而使得对微生物空间分布格局及其成因的深入研究成为可能。进而可以从方法学探讨微生物生物多样性、分布格局、影响机制及其对全球变化的响应等。在微生物生态学研究中,群落构建与演化、分布特征(含植物-微生物相互关系)、执行群体功能的机理(生物地球化学循环等)、对环境变化的响应与反馈机理是今后需要关注的重点领域。概述了微生物生态学的概念,并初步提出其理论框架,在对比宏观生态学基础理论和模型的基础上,分析微生物多样性的研究内容、研究方法和群落构建的理论机制,展望了今后研究的重点领域。     

大仓鼠种群遗传多样性的季节性变化

通过随机扩增多态性DNA（RAPD）方法,我们对河北省固安县牛驼镇王龙村附近的大仓鼠（Cricetuls triton)种群的遗传多样性进行了研究。结果显示,在209个大仓鼠个体中（春季60只,夏季45只,秋季59只,冬季45只）,共扩增出87条带,其中86．2%原条带具有多态性,4个季节种群的遗传组成存在季节变化,其多态位点数,多态位点比率,Shannon多样性指数及Nei指数的大小顺序均一致表现为：秋季种群＜冬季种群＜夏季种群＜春季种群;秋季种群的遗传多态性最低,春季最强;遗传多态性与种群密度（夹捕率,％）,之间呈极显著的负相关关系。此结果表明遗传因素与大仓鼠种群动态有密切关系,但季节间遗传多态的变化不支持Ford假说,我们认为增殖和扩散共同决定了季节间遗传多样变化的规律。     

大石鸡边缘种群的遗传结构

大石鸡（Alectoris magna）分布于青海西部、东部,甘肃中部和宁夏西部的干部和半干旱区,由于环境变化,其种群向甘肃南部森林被砍伐的地区扩散,形成涟缘种群。本研究采用聚合酶链式反应（PCR）和直接测序的方法获得了采自甘肃的大石鸡一个边缘种群和两个中心地理种群共39个个体的线粒体DNA（mtDNA）控制区基因（D－loop）456－457个核苷酸的基因序列,16个变异位点（占整个序列的3.5%）有15个单倍型。边缘扩散种群有3种单倍型,M6与另两个种群共有,单倍型频率为0.108,而M4和M5为其特有,单倍型频率分别为0.081和0.027。边缘种群的单倍型比率和遗传多样性分别为37.5%和0.549。中心地理种群1和种群2各有7个单倍型,除M6炳种群共有,其余为自所特有,单倍型比率分别为46.7%和50.0%,遗传多样性分别是0.729和0.786。边缘种群的单倍型比率和遗传多样性均低于中心地理种群。     

中国大鲵四种群的遗传结构和地理分化

为了确定栖息地的破碎化和片断化引起中国大鲵的地理分化和遗传结构变异,本文测定了来自广西、河南、陕西和湖南4个地理种群的28条大鲵的mtDNAD loop基因全序列。根据这4个地理种群的地理分布,分成珠江单元(广西种群)、黄河单元(河南种群)和长江单元(湖南和陕西种群)。通过ClustalX、MEGA2.0、DnaSP4.0、Arlequin1.1分析发现,全序列长度为771bp,其中64个多态性核苷酸变异位点,占全部碱基数的8.26%。转换和颠换分别为6和2个,插入/缺失11个。27个单倍型间的序列差异平均为1.32%。3个单元的单倍型多样性指数和核苷酸多样性指数值都偏低,而且珠江单元的这两个指数值都低于长江和黄河两个单元。珠江单元和黄河、长江单元之间分化程度显著(P<0.001),而长江和黄河单元之间差异不显著(P>0.05)。地理单元内分化程度占99.31%,而单元间只有0.69%,表明遗传差异主要发生在单元内,而且各地理单元之间的基因流较频繁。构建的NJ树和MP树显示,27个单倍型呈现一种混杂的分布格局,并未分成代表3个地理单元的聚合群。     

独龙牛遗传多样性及其种群遗传结构的等位酶分析

采用水平片淀粉凝胶电泳技术,进行３０头独牛牛４１种蛋白质共计４４个遗传座位的等位酶分析,只在Ｔｒ,Ｈｐ,Ａｍｙ,Ｅｓｔ等４个座位发现多态性。每个座位等基因的平均数、多态座位百分比和平均杂合度值分别为Ａ＝１．０９０９、Ｐ＝０．０６８２和Ｈ＝０．０２６２。贡山县和福贡县独龙牛群体从酶基因的角度上看遗传多样性贫乏,可能是分别由小种群引种而来,受到瓶颈效应的作用,并伴随着创立者事件的发生。我们结合独龙牛在     

通用选择指数原理

本文在对各类种畜评定方法探讨的基础上,提出了通用选择指数概念,对各类评定方法在理论上加以综合,推导出统一的计算公式,并编制出相应的计算程序。为充分利用种畜各种信息,特别是为在多信息来源需作约束、最宜选择时的种畜评定,提供了行之有效的计算方法。避免了在实际应用时对各类评定方法的独立探讨以及因多种计算体系导致应用上的混乱。此外,本文还得出了有关选择理论的三个结论,并改正了文献[2]中的失误之处。     

A Multistage Load Distribution Strategy for Three-Dimensional Meshes

We study the problem of scheduling a divisible load in a three-dimensional mesh of processors. The objective is to find partition of a load into shares and distribution of load shares among processors which minimize load processing time subject to communication delays involved in sending load from one processor to another. We propose a new scheduling algorithm which distributes load in a sequence of stages across the network, each stage brings load to a set of processors located at the same distance from the load source. A key feature of our solution is that sets of processors receive load in the order of decreasing processing capacities. We call this scheduling strategy Largest Layer First. A theorem about the processing time attained by the algorithm is stated. Performance of the algorithm is compared to earlier results.     

A Novel Theory on the Origin of the Genetic Code: A GNC-SNS Hypothesis

We have previously proposed an SNS hypothesis on the origin of the genetic code (Ikehara and Yoshida 1998). The hypothesis predicts that the universal genetic code originated from the SNS code composed of 16 codons and 10 amino acids (S and N mean G or C and either of four bases, respectively). But, it must have been very difficult to create the SNS code at one stroke in the beginning. Therefore, we searched for a simpler code than the SNS code, which could still encode water-soluble globular proteins with appropriate three-dimensional structures at a high probability using four conditions for globular protein formation (hydropathy, α-helix, β-sheet, and β-turn formations). Four amino acids (Gly [G], Ala [A], Asp [D], and Val [V]) encoded by the GNC code satisfied the four structural conditions well, but other codes in rows and columns in the universal genetic code table do not, except for the GNG code, a slightly modified form of the GNC code. Three three-amino acid systems ([D], Leu and Tyr; [D], Tyr and Met; Glu, Pro and Ile) also satisfied the above four conditions. But, some amino acids in the three systems are far more complex than those encoded by the GNC code. In addition, the amino acids in the three-amino acid systems are scattered in the universal genetic code table. Thus, we concluded that the universal genetic code originated not from a three-amino acid system but from a four-amino acid system, the GNC code encoding [GADV]-proteins, as the most primitive genetic code. Received: 11 June 2001 / Accepted: 11 October 2001     

The General Theory of Mapping Functions for Random Genetic Recombination

The general theory of mapping functions for random genetic recombination is derived without reference to physical models. The results are of particular relevance to asymmetric recombination (preferential recombination of the alleles of either parent) and include the effects of lethal lesions. It is noted that the assumption of randomness determines the mapping functions uniquely so that they are independent of the specifications of any stochastic physical model of recombination. In particular, the functions derived from physical models by Haldane, Wu, Wood and Verhoef and de Haan are special cases of those derived here. A general principle for the testing of genetic linkage is formulated which is valid for both symmetric and asymmetric recombination.     

A Unique Genetic Distance

The problem of measuring distances between discrete frequency distributions is considered. Three conditions are stated, which are believed to reflect basic, intuitive requirements to be met by a distance measure of the above kind with particular reference to genetic frequency distributions. These conditions chiefly concern aspects of maximum distance and linearity. It is shown that exactly one function meets the conditions, and this function, having all properties of a metric, is explicitly given.     

Divisible Load Theory: A New Paradigm for Load Scheduling in Distributed Systems

Divisible load theory is a methodology involving the linear and continuous modeling of partitionable computation and communication loads for parallel processing. It adequately represents an important class of problems with applications in parallel and distributed system scheduling, various types of data processing, scientific and engineering computation, and sensor networks. Solutions are surprisingly tractable. Research in this area over the past decade is described.