第七章 回交育种要点

第七章 回交育种7.1 The significance and genetic effect ofbackcross breedingConceptConceptConcept•Backcross•Backcross breeding:•the method of introducing thetarget traits of the donor intothe recipient through one or [ (A×B)×A ]×A ......more backcrossesConcept Concept Concept•Recurrent parent:•Parents used for multiplebackcrossing are called Recurrent parents •Non-recurrent parent:•Parents used only in the firsthybridization are called non-recurrent parents[ (A×B)×A ]×A ......Recurrent parent Non-recurrent parentConcept Concept Concept•Receptor parents:•Accepts favorable traits (target traits)•Donor parent:•provides of target traits•1) recovery of recurrent parent (selection of recurrent parent is critical) – Forward selection•2) incorporate a new trait from the donor parent-BackgroundThe significance of backcross breeding•Backcross breeding is the most effective method for improvingmaterials with good comprehensive traits but few unfavorabletraits, especially the unfavorable traits have high heritability(quality traits or main effect QTL)•Backcross breeding can effectively overcome the problems ofhybrid sterility and too long separation period in wide-crossbreeding•Backcrossing helps to break the genetic linkage dragGenetic effects of backcrossing•The genotype homozygous rate of backcross offspring was consistent with that of self-cross; ex: BC4, (25-1)/25 = 31/32 or 96.875%•The homozygous genotype of backcrossing offspring is controlled by the recurrent parent and is not completely consistent with thehomozygous direction of self-crossing offspring•Backcross is conducive to eliminate the probability of linkage drags7.2 Key points of backcross breedingSteps of the key pointsThe selection for the parentsThe selection for the offspringThe number of backcrossesperformed7.2.1 The selection for the parents•Recurrent parents:üHave good comprehensive traits üHave expected utilization value •Non-recurrent parents:üProvide target genesüNo serious shortcomings7.2.2 The selection for the offspringsBackcross and transfer of qualitative traits :ØTrait transfer controlled by a pair of dominant genesØTrait transfer controlled by a pair of recessive genesØTransfer of a dominant gene is accomplished more readily than arecessive gene Backcross transfer of quantitative traits ØPolygene; it takes long timeØDue to the influence of environment, progeny test is necessary, and sometraits need to create favorableenvironments for identificationØIncrease the population size to ensure that each backcross generation canappear the target genotypesØCombined with marker-assisted selectionTransfer of a dominant gene using backcrossing.Source: Stoskopf, 1993.Plant Breeding Theoryand Practice.Transfer of a recessive gene using backcrossingSource: Stoskopf, 1993.Plant Breeding Theory andPractice.7.2.3 The number of backcrosses performedØThe importance of recovering the traits of the recurrent parent ØThe number of selected plants during backcrossingØThe similarity between the recurrent and donor parentsØLinkage drags between desirable and undesirable genes7.3 The methods derived from backcross breedingFour main methods of backcrossingStepwise backcrossing Pedigree backcrossingDouble backcrossing Convergent backcrossing7.3.1 Stepwise backcrossingØWhen the target traits come from different donors, the backcross between the recipient parents and different donors can be carried out step by step, which is called stepwise backcrossing method.7.3.2 Pedigree backcrossingØIn order to enlarge the genetic influence of a parent on hybrid offspring, the parents and hybrid offspring can be backcrossed 1-2 times, and then the breeding can be continued by genealogyØIncomplete backcrossing of 1-2 times is also called limitedbackcrossing method7.3.3 Double backcrossingØWhen two parental inbred lines A and B of A superior singlecross A/B have better comprehensive traits and combining ability, but each has different defectsØThe defect of A can be overcome by B, and the defect of B can be overcome by A7.3.4 Convergent backcrossingØWhen the target traits come from more donors, the modified varieties and multiple donors can be backcrossed for several generations at the same time, and then the improved lines with the unique excellent traits of each donor parent can be selected and bred by multiple-hybridizations7.4 The characteristics and application of backcross breedingAdvantages of Backcross BreedingØPredictable - traits of the recurrent parent are recovered with one new trait introgressed.ØAn existing cultivar can be improved without risk of breaking up desirable gene combinations.ØThe location where the backcrossing procedure is conducted is independent of the area of adaptation.ØLess testing is required prior to releaseDisadvantages of Backcross BreedingØThere is no possibility of a desirable new recombination of traitsØNot useful in quantitatively inherited traits such as horizontal disease resistanceØLinkage drags may reduce the recovery of the recurrent parentgenotypeOther uses for backcrossingüDevelopment of isogenic lines or isolines or near-isogenic lines(lines differing from one another for only one trait)üBreeding multi-line varietiesüDevelopment of cytoplasmic male sterile lines1) Backcrossing “transgenes” into different backgrounds.2) Molecular markers are used to assist in backcrossing in TWO ways- to select for the gene of interest- to select plants with the least amount of DNA from the donor parent. (Markers spaced out over the entire genome)。

第七章回交育种
一学时数：2
二教学目标：
使学生了解回交的遗传效应和回交育种步骤；重点掌握显性单基因、隐性单基因目标性状回交转育的工作内容；回交的用途。

三教学重点：显性单基因、隐性单基因目标性状回交转育的步骤
四教学难点：回交的遗传效应
五教学内容及教学过程：
1.复习杂交育种重点内容，导入新课，讲述回交育种的概念；以及轮回亲本和非轮回亲本、供体亲本与受体亲本的概念；回交育种的应用条件。

10min.
2. 利用公式、表格讲述回交的遗传效应：轮回亲本的基因频率逐渐增加，非轮回亲本的基因频率逐渐减少；回交后代达到一种纯合基因型的速度更快；可以更有效地打破不利基因的连锁。

10min.
3.讲述回交育种工作包括杂交、回交、选株连续回交、自交稳定和产量比较五个环节的基础上，分别讲述与回交育种过程相关的轮回亲本、非轮回亲本的选择指标；回交的次数；回交所需的植株数等问题。

20min.
4. 结合回交育种程序，讲述显性单基因和隐性单基因控制性状的回交转育步骤；比较两类性状回交转移步骤地异同。

20min.
5. 明确对多个目标性状的导入可采用逐步回交和聚合回交的方法，图示说明聚合回交的两种策略。

15min.
6. 通过与杂交育种的对比，总结回交育种的优势和局限性。

10min.
7. 阐述回交的用途，除了用于改良品种的个别缺点的作用外，还可用于近等基因系的培育、雄性不育系的转育和克服远缘杂交困难等方面。

13min.
8. 小结，布置思考题。

2min.。

《植物育种学》第七章回交育种复习题及答案一．选择题1）下列不是回交的表示方式的是________（以AB表示两亲本）（C）A. [（AxB）xA]xAB. A 3xBC. AxBxAxAD. A3 /B2）轮回亲本应具有的特点________（B）①适应性强②产量高③良好的农艺性状④改良后仍有发展潜力⑤只存在个别缺点⑥可以和不利基因有一定的连锁A. ①②③④⑤⑥B. ①②③④⑤C. ③④⑤D. ①②⑥3）基因纯合率公式是________（D）A. （1-1/2r）n-1B. （1-1/2r-1）nC. （1-1/2r-1）n-1D. （1-1/2r）n4）下列不是非轮回亲本应具有的特点的是_______（A）A. 目标性状突出，适应性强B. 目标性状不与不良基因连锁C. 具有改进轮回亲本所需要的性状或基因D. 目标性状突出，最好是显性5）以下哪一个是以A亲本为轮回亲本的回交育种______ （D）A. AXBXCB. (AXB)XBC. AXBXBD. A/B//A6）回交育种要求改良后仍具有发展潜力，要求在_______ 年内。

（C）A. 2~3B. 3~4C. 5~6D. 7~87）回交育种中，控制需要转育的目标性状的基因数目为一对，则回交一代出现带有所需目标基因的个体频率为______（B）A. 1/3B. 1/2C. 1/4D. 1/88）回交育种所利用的亲本不包括（B）A. 优质品种B. 高干亲本C. 轮回亲本D. 非轮回亲本9）回交育种法中，目标性状的提供者称为（B）A. 轮回亲本B. 非轮回亲本C. 母本D. 父本10）回交育种法中，目标性状的接受者者称为（A）A. 轮回亲本B. 非轮回亲本C. 母本D. 父本11）既可以保持亲本基本性状，有可以添加特定的目标性状，再通过筛选而培育出新品种的育种方法是（C）A. 引种B. 杂交育种C. 回交育种D. 诱变育种12）回交育种中，无论回交次数多少，最后都得（D）A. 杂交B. 测交C. 选择D.自交13)回交后代的杂种群体已具有目标性状与轮回亲本优良性状基本相似时，为选择显性性状纯合个体，需自交次；隐性性状纯合个体需自交次（B）A. 1 , 1B. 2 ，1C. 1 ，2D. 2 ，214）回交育种法可以在、加代中进行回交和选择，缩短育种年限。

第一章1、如何测定作物的自然异交率㈠测定授粉方式的方法①确定授粉的方式（花器构造、开花习性等)②人工自交观察衰退情况(套袋,强迫自交)③测定异交率(4%以下是典型自花授粉作物.50~100%典型的异花授粉作物.4~50%常异花授粉作物）㈡①父本--显性标志性状.母本---相应隐性性状②父母本行间种植或父本种在母本周围③收母本植株种子播种㈢F1中显性性状个数∕F1总个体数﹡100%2、自交和异交的遗传效应自交的遗传效应:①杂合的基因型趋向纯和②后代发生性状分离③后代生活力衰退异交的遗传效应:①形成杂合基因型②后代生活力增强3、作物品种的类型及含义DUS①特异性:本品种具有一个或多个不同于其它品种的形态②一致性:品种内同株性状整齐一致③稳定性:品种的特异性和一致性在繁殖后保持不变4、各类品种的育种特点①自交系(纯系)品种a创造遗传变异丰富和性状分离的大群体,从中进行单株选择b自花授粉结合单株选择,即连续自交下选择纯和优良基因型②杂交种a自交系育种b杂交组合育种③群体品种a对后代群体一般不进行单株选择b保持较大的随即样本群体,多代自由授粉下积累有益基因改良群体④无性系品种a有性杂交+无性繁殖b利用芽变5、.不同授粉方式作物的遗传特点及育种方法（一）自花授粉作物：如水稻、小麦、大麦、燕麦、大豆、绿豆、豌豆、花生、异交率为0~4%。

花器构造特点①是两性花, 雌雄蕊同花、同熟，二者长度接近或雄蕊较长；②开花时间较短，甚至闭花授粉；③花器保护严密，其他花粉不易飞入。

遗传特点：⑴个体基因型纯合⑵群体内基因型单一⑶群体内个体之间表现型整齐一致(4)遗传稳定育种与良繁方法：⑴利用自然变异和天然异交⑵人工强迫异交与单株选择相结合------杂交育种⑶人工强迫异交-------杂优利用（不易去雄）⑷良繁时隔离距离要求不严格，适当隔离。

(二) 异花授粉作物：异交率>50%，甚至高达95%或100%。

代表作物：玉米，大麻，菠菜，黄瓜，甘薯等。

《植物育种学》（杨存义）绪论一、名词解释1. 作物品种：是人类在一定的生态条件和经济条件下，在产量、抗性、品质等方面都能符合生产发展的需要，根据人类的需要所选育的某种作物遗传特性稳定、性状一致、特性明显的一定群体。

2．优良品种是指在一定地区和耕作栽培条件下符合生产发展要求，并具有较高经济价值的品种。

二、填空题1．每个作物品种一般都有其所适应的地区范围和耕作栽培条件，而且都只在一定历史时期起作用，所以优良品种一般都是具有地区性和时间性。

2．作物品种可分为纯系品种、杂种品种、综合品种、五性系品种。

3. 作物进化决定于3个基本因素：变异、遗传、选择。

三、简答题1．优良品种在发展农艺生产中的作用主要有：1）提高单位面积产量2）改进产品品质3）保持稳产性和产品品质4）扩大作物种质面积5）有利于耕作制度的改良、复种指数的提高、农业机械化的发展及劳动生产率的提高。

2．作物育种学的基本任务是什么？1）研究和掌握作物性状遗传变异规律的基础上，发掘、研究和利用各有关作物资源；2）并根据各地区的育种目标和原有品种基础，采用适当的育种途径和方法，选育适于该地区生产发展的高产、稳产、优质、抗（耐）病虫害及环境胁迫、生育期适当、适应性较广的优良品种或杂种以及新作物；3）在其繁殖、推广过程中，保持和提高其种性，提供数量多、质量好、成本低的生产用种，促进高产、优质、高效农业的发展。

3．作物育种学的主要内容：1）育种目标的制订及实现目标的相应策略；2）种质资源的搜集、保存、研究评价、利用及创新；3）选择的理论与方法；4）人工创造变异的途径、方法和技术；5）杂种优势利用的途径和方法；6）目标性状的遗传、鉴定及选育方法；7）作物育种各阶段的田间实验技术；8）新品种的审定、推广和种子生产。

4．现代作物育种的发展动向主要表现在以下几方面：1）育种目标要求要高。

现代农业对新品种不仅要求进一步提高单产潜力，增强对多种病虫害及环境胁迫的抗耐性，广泛的适应性；而且还要求具有优良的产品品质和适应机械操作的特性等。