Chapter 12 Inheritance analysis of q uantitative character 数量性状遗传分析

1. Chapter 12 Inheritance analysis of quantitative character数量性状遗传分析 Traits that exhibit quantitative phenotypic variation are often under the genetic control of alleles whose influence is additive in nature, resulting in continuous variation. Such traits can be analyzed and characterized using statistical methods Discontinuous variation and continuous variation Discontinuous variation: Qualitative character, the resultant phenotypic variation was classified into distinct traits For example：pea flower color, squash fruit shape Continuous variation: Quantitative character, the resultant phenotypic are not as easily categorized into distinct classes For example: human height, fruit size et al 由表现累加效应的等位基因控制并可度量的连续变异的性状 非连续变异和连续变异 非连续变异：表型变异是可区分的，数量性状：豌豆花的颜色，南瓜果形 连续变异：产生的表型是不可区分的，数量性状：人的身高，果实大小

2. Continuous variation连续变异

3. Introduction of quantitative inheritance数量性状遗传 1.Traits exhibiting continuous variation, including some important economic traits such as yields of milk, corn, and beef, are most often controlled by two or more genes that provide an additive component to the phenotype that can be quantified 2. Quantitative traits were difficult to study, and their mode of inheritance was not classified until in the 20th century. 3. Because these results were exceptions to the patterns observed by Mendel in most of his crosses, they failed to support his hypotheses and no doubt delayed the acceptance of his work 一、数量性状表现为连续变异的性状，包括一些重要的经济性状，如牛奶，玉米和牛肉的产量，通常由两个或更多具有累加效应的基因控制，表型可量化 二、20世纪以前，因为它们的遗传方式不明确，很难研究数量性状 三、由于这些性状的研究结果不符合孟德尔的比率，也不支持他的假说，这无疑影响了人们对孟德尔理论的接受

4. The multiple factor hypothesis Variation of tobacco plant in height烟草植株高度的变异

5. Experiment of tobacco cross烟草杂交实验

6. Character of the distribution of F2 data子二代的数据分布特点 The F2 data demonstrate a normal distribution , as evidenced by the bell-shaped curve in the bottom histogram 下面的直方图表明F2的数据呈正态分布

7. Edward M. East’s experiment Edward M. East 试验 • He crossed two true breeding strains of the tobacco plant, the corollas of strains A is shorter than that of strains B • 利用两个真实遗传的烟草植株进行杂交繁殖，植株A的花冠比植株B的花冠短 • strains A × strains B • ↓ • F1(immediate) • ↓ • F2(many variation between two strains)

8. Figure of tobacco corolla烟草花冠图

9. The F1 and F2

10. The variation of F3 plants in different F2 famlies来源于不同的F2株系的F3植株变异

11. The significance of this experimentEdward M. East 实验的意义 East’s experiments demonstrated that although the variation in corolla length seemed continuous, experimental crosses resulted in the segregation of distinct phenotypic classes as observed in the three independent F3 categories. The key finding was the basis for the multiple-factor hypothesis Edward M. East 的实验结果表明，虽然花冠长度的变异似乎是连续的，杂交实验也产生了不同类型表型的区别，如在F3出现三个独立的类别。这一关键发现是多基因假说的基础

12. The content of multiple-factor hypothesis多基因假说要点 1. Continuous trait can be quantified by measuring, weighing, and counting 2. Two or more pairs of genes influence on the phenotype in an additive way 3. Each gene locus may be occupied by either an additive allele or non-additive allele 4. The total effect on the phenotype of each additive allele, while small, is approximately equivalent to all other additive at other gene site 5. Together , the genes controlling a single character produce substantial variation 6. Analysis of polygenic traits requires the study of large numbers of progeny from a population of organisms 7. Like major genes, minor genes is on chromosomes and exhibit the genetic characteristics such as disjunction, recombination, linkage and so on 一、连续变异的性状可以通过测量、称重、计数来量化。 二、两对或更多的基因通过累加的方式影响表型 三、每一基因位点可由加性等位基因或非加性等位基因占据 四、每个基因对表型的作用是微小且近乎相等的， 五、很多基因合在一起才能产生实质性的变异 六、多基因性状的分析需要从群体的角度研究大量后代 七、微效基因与主效基因一样位于染色体上，具有分离、重组和连锁等性质

13. Herman Nilsson-Ehle’s experimentsHerman Nilsson-Ehle实验

14. Punnett square

15. Two pairs of genes

16. Binomial methods • A event： F2 the probability of R(R1or R2)， p=1/2 • B event： F2 the probability of r(r1or r2)， q=1/2 • n = 4，the number of heterozygous gene

17. Two pairs of genes

18. Three pairs of genes

19. Binomial methods--three pairs of genes • A event：F2 the probability of R(R1, R2 or R3)，p=1/2 • B event：F2 the probability of r(r1, r2 or r2)， q=1/2 • n=6，the number of heterozygous gene • Note: n equals double of the number of the gene pairs

20. The relationship between gene pairs and phenotypes基因对和表型之间的关系

21. Calculating the number of genes计算基因的数量 1/4n = ration of F2 individuals expressing either extreme phenotype 在F2代个体中表现极端表型的机率

22. Threshold character阈性状 Traits that exhibit discontinuous phenotypic variation are under the genetic control of minor genes, which are classified as two categories For example：Living versus death, the ill versus the normal 1. The concentration of a substance or development velocity to control the trait potentially exhibit continuous variation, generally a normal distribution For example: The concentration of a antibody to contron liability in human is classified as the ill versus the normal by a threshold value 2. Discontinuous phenotypic variationcan be calculated For example: Litter size 阈性状是由多基因决定而表型是非连续的一类性状，如“存活与死亡”、“患病与正常”，它有两类分布 一、造成该类性状的某种物质浓度或发育过程的速度的潜在的连续分布，多呈正态分布。对于此类“阈性状”的理解：如与人的易患呈平行关系的抗体物质浓度被一个“阈值”（如20%）区分出一个不连续的“发病”与“正常”两部分 二、表型的间断分布（P）：可计数，如每胎产仔数

23. Genetic analysis of polygenic traits数量性状的遗传分析 • To assess the validity of the experimental data, statistical techniques are used • 使用统计技术评估实验数据的有效性

24. Mea--平均数 • Mean( )is the clustering of central tendency, and the simply the arithmetic average of a set of measurements or data • 平均数是表示样本观察值的集中程度，可简单作为数据资料的算术平均数

25. Variance--方差 • Variance shows the degree to which values within this distribution diverge from the mean and is used to estimate the variation present in infinitely large population • Variance, V / S2 • V＝Σ(Xi－X )2/N • 方差表示变量离开平均数的变异程度，用于估计无限大群体的变异

26. Standard deviation--标准差 • Standard deviation is the square root of the variance, and is used to express variation around the mean in the original units of measurement • Standard deviation, S / Sd • 标准差是方差的平方根，以原有的计量单位表示数据偏离平均数的变化程度

27. Standard error of the mean平均数标准误差 Standard error of the mean measures the accuracy of the sample mean—that is, the variation of sample means in replications of the experiment, and is used to estimate how much the means of other similar samples drawn from the same population might vary

28. Heritability--遗传力 • Phenotype is controlled by genes and environment • P = G + E • P ：phenotypic value of individual (observed value) • G：genetic value of individual • E：environment value 表型是受基因和环境的共同作用 G：性状的基因型值 E：环境效应值 P：性状的表型值

29. Division of genetic effect基因型值的剖分 • In quantitative traits controlled by many pairs of genes, genetic values in segregating population can be divided into three classes A, additive effect：the variation caused by all alleles and non-alleles D, dominance effect：the variation caused by dominant gene I, epistatic effect：the variation caused by non-allelic gene Hence：G = A + D + I  P = A + D + I + E D and I are called non-additive effects • 多对基因控制的数量性状，分离群体的基因型值可分离为三类。 加性效应：等位基因和非等位基因产生的效应 显性效应： 显性基因产生的效应 上位效应： 非等位基因产生的效应 因此：G = A + D + I  P = A + D + I + E

30. Division of variance方差分量 Variance can be divided into: VP = VG + VE • VP: phenotypic variance • VG: caused by different genotypes in population，called genetic variance • VE: environment variance • VP表型方差 • VG遗传方差 • VE环境方差

31. Division of genetic variance遗传方差分量 • Three genetic variance exist： • VA：加性方差 • VD：显性方差 • VI：互作方差 • Hence：VG = VA + VD + VI • VP = VA + VD + VI + VE • Both VD and VI are called non-additive variance • VD和 VI是非加性方差

33. Broad--sense heritability • Broad sense heritability refer to the proportion of genetic variance to total variance. hB2： • 广义遗传率是指遗传变异占总变异的百分率

34. Size of hB2广义遗传力大小 • The size of hB2 varies from 0 to 1.0 • An hB2 value approaching 1.0 indicates that environmental conditions have little impact on phenotypic variance in the population studied • An hB2 value approaching 0 indicates that the environment is almost solely responsible for the observed phenotypic variation • 广义遗传率的大小从0到1 • 一个hB2值接近1.0表明，环境条件对群体的表型变异影响很少。 • 一个hB2值接近0表明，观察到的表型变异几乎完全是环境的影响结果

35. Narrow- sense heritability狭义遗传力 • Narrow-sense heritability refer to the proportion of additive variance to total variance. hN2： • 狭义遗传力指的是加性方差占总方差的比率

36. Environmental variance is estimated with non-segregating populations’varianceVP1, VP2, VF1 Genetic variance:VG=VP-VE' Phenotypic variance is estimated with F2 populations’ variance VF2 So the formula of hB2 is: Estimation of hB2广义遗传力的估算

37. Estimation of hN2狭义遗传力的估算 The defined formula of hN2 VP'= VF2 = VA + VD + VI + VE

38. Close breeding • Inbreeding: Close breeding or consanguineous mating, mating that individuals with blood relationship cross each other. The individuals with more than one common predecessors are called the relative • Coefficient of relationship(R): A measurement of the blood relationship between individuals • For example: • The first relative(R=1/2): parents, full-siblings • The second relative(R=1/4): Uncles, aunts, and (maternal)grandfather(mother) • The third relative(R=1/8): Cousins, grand-grandfather(mother) • Coefficient of inbreeding(F): Coefficient of genetic relationship between mating gametes; that is, the possibility occurres in a specific locus for a individual which receives two alleles with the same genetic relationship • F = ½ R • Consanguineous mating results in homozygous genotypes • Path and path link: A arrow line linking the cause and result is called path. The effect of a cause on the result is called path coefficient. The whole passage consisted of more than one path is called path link

39. 近亲繁殖 近交：也称近亲繁殖或近亲交配，是指有亲缘关系的个体互相杂交的交配形式。具有一个或一个以上共同祖先的个体称为亲属 近交系数（F）：结合的配子间的遗传相关系数，指个体在一个特定的基因座位上接受两个遗传上（或者说血缘上）相同的等位基因的概率 亲缘系数（R）：个体间亲属关系的度量 一级亲属（R=1/2）：双亲与其子女、全同胞 二级亲属（R=1/4）：叔、伯、姑、舅、姨、（外）祖父母 三级亲属（R=1/8）：表兄妹、堂兄妹、曾祖父母 F = ½ R 近交的结果是导致基因的纯合 通径与通径链：连接原因与结果的每一个单箭头线条为通径；一条通径中原因对某一结果所起作用的相对大小即通径系数；由一条或一条以上通径所组成的完整通道称为通径链

40. Calculating coefficients of inbreeding近交系数的计算 Selfing(自交)：F = 1/2 Other inbreeding(其它近交): a1a2 a3a4 Calculating based on the possibility of gametes(以配子概率推算)： A B The possibility of a1a1 in K(得到a1a1的概率)： C D （1/2）4 x （1/2）3=（1/2）7 G H The possibility of any homozygous genotypes(任何一对基因纯合的概率)： J 4 x （1/2）7=1/32 K

41. The path way to calculate coefficients of inbreeding通路法计算近交系数 • One can calculate the linked pathes from the individual to calculate its coefficient of inbreeding to itself via the parental predecesssors • 从欲计算近交系数的个体出发，通过他两个亲本的共同祖先，再返回到这个个体，计算相连的通路 • Path1(通路1)：K-J-G-C-A-D-H- • Path2(通路2)：K-J-G-C-B-D-H- • There are 6 steps in the two pathes in all（两条通路共有6步） • Coefficients of inbreeding(近交系数)：F=2 x（1/2）6=1/32

42. Effect of inbreeding近交效应 • 1. Inbreeding decreases the mean of genotype values in a population while hybridization increases it • 2. Inbreeding differentiates a population while hybridization leads to consistent heretozygotes in a population • 3. Inbreeding combined with artificial selection is one of approaches to enhance heterosis • 一、近交降低群体基因型值的平均值，杂交提高群体均值 • 二、近交使群体分化，杂交使群体一致 • 三、近交与人工选择相结合是提高杂种优势的重要手段之一

43. Heterosis--杂种优势 Heterosis: In members of two favorable inbred lines are often more vigorous in desirable traits than either of the parental lines, which is called hybrid vigor Dominant hypothesis: The F1 hybrids are heterozygotes at all loci shown. The deleterious recessive alleles present in the homozygous form in the parents is masked by the more favorable dominant alleles in the hybrids. Over-dominant hypothesis: It holds that in many cases the heterozygote is superior to either homozygote. This may relate to the fact that in the heterozygote two forms of a gene product may be present, providing a form of biochemical diversity. Thus, the cumulative effect of heterozygosity at many loci accounts for the hybrid vigor 杂种优势：由两个自交系亲本杂交产生的杂种的目标性状优于双亲的现象 显性假说：杂种优势是由于双亲的显性基因集中在杂种中所引起的互补作用 超显性假说：杂种优势来源于双亲基因型的异质结合所引起的基因间的互作