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Chapter 3 Genetic analysis of l inkage and chromosome mapping

Chapter 3 Genetic analysis of l inkage and chromosome mapping. Key points: 1. Sex-chromosome and sex determination 2. Linkage versus independent assortment 3. Incomplete linkage 4. Mapping in Drosophila and maize 5. The accuracy of mapping experiments

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Chapter 3 Genetic analysis of l inkage and chromosome mapping

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  1. Chapter 3Genetic analysis of linkage and chromosome mapping • Key points: • 1. Sex-chromosome and sex determination • 2. Linkage versus independent assortment • 3. Incomplete linkage • 4. Mapping in Drosophila and maize • 5. The accuracy of mapping experiments • 6.The genetic map of drosophila • 7.Somatic cell hybridization and human gene mapping

  2. Section 1 Sex-chromosome and sex determination • 1. The discovery of sex-chromosomes • 2. types of sex determination. Basically, four type of chromosomal sex-determining mechanisms exist; the XY, ZW, X0, and compound chromosomal mechanism: • (1) The XY system: male(XY), female(XX). Including humans, mammals, some amphibians and fish, as well as many insects and dioecious plants, etc. • (2) The ZW system: male(ZZ), female(ZW). Including birds, Lepidoptera, some amphibians, reptiles, and Silkworm • (3) XO system: male(XO), female(XX). Including Orthoptera insects such as grasshoppers and cockroach • Some animals such as Bniella, their sexes are determined by environment factors

  3. 第一节 性染色体与性别决定 • 一、性染色体的发现 • 二、性别决定的几种类型 • 1、 XY型：雄性：XY、雌性：XX。人类、哺乳类、某些两栖类和某些鱼类，以及很多昆虫和雌雄异株的植物等 ) • 2、 ZW型： 雄性：ZZ、 雌性：ZW。鸟类、鳞翅目昆虫、某些两栖类、爬行类动物及家蚕 • 3、 XO型：雌体的性染色体为XX，雄性只有一条单X染色体，为XO， 如一些蚱蜢和蟑螂 • 有些动物的性别决定依赖于环境因素，如后嗌

  4. Section 2 Sex-linked inheritance 第二节 性连锁遗传---果蝇伴性遗传研究

  5. Sex-linked inheritance • When homozygous dominant genes are passed with homogametic-sex individuals, dominant characters are expressed in both male and female individuals in the F1 generation. In the F2 generation, the separation proportion of dominance versus recessiveness is 3:1 and that of sex 1:1. The meternal grandfather passes the character to his grandson • 2. When homogametic-sex individuals pass homozygous recessive genes to their offspring, the criss-cross inheritance exihited in the F1 generation; that is, the mother passes traits to her son and the father to his daughter. In the F2 generation, the separation ratio of traits and sexes is 1:1 • 3. The transmission and expression of genes located on sexual chromosomes are dependent on sexes. Results of reciprocal crosses show differences in phenotypic ratios in both F1 and F2 generations

  6. 性连锁遗传---伴性遗传的特点 • 1、当同配性别传递纯合的显性基因时，F1雌雄个体都为显性性状；F1性状的分离呈3显性：1隐性；性别的分离呈1：1，其中隐性个体的性别与祖代隐性体一样，即外祖父的性状传递给外孙 • 2、当同配性别传递纯合的隐性基因时，F1表现交叉遗传，即母亲把性状传给儿子，父亲的性状传给女儿，F2性状与性别的比均为1：1 • 3、决定性状的基因在性染色体上；性状的遗传与性别有关；正交与反交F1的结果不同；表现特殊的交叉遗传规律。

  7. Figure of sex-linked inheritance in humans 性连锁遗传---人类的伴性遗传图示 X-linked inheritance disorders: Anti-VD rickets, Color blindness, hemophilia With Y-linked inheritance: Hairy-eared edge 伴X连锁遗传： 抗VD佝偻病，色盲，血友病 伴Y连锁遗传：毛耳缘

  8. The pedigree of human color blindness

  9. Figure of X-linkage in Drosophila 果蝇性连锁遗传图

  10. Example of sex-limited inheritancechicken鸡的伴性遗传

  11. Section 3 The direct evidence of chromosome theory of heredity 第三节 遗传的染色体学说的直接证明

  12. Section 4 Y chromosome and sex determination in Drosophila The critical factor in determining sex is the ratio of X chromosomes to the number of haploid sets of autosomes (A) present: 1. when X \ A = 0.5, the male 2. when X \ A = 1, the female 3. when the ratio of X \ A ranges 0.5 from 1, the intersexual

  13. Drosophila

  14. 第四节 果蝇中的Y染色体及其性别决定 • 果蝇的性别决定并不取决于X和Y 染色体，而取决于性染色体和常染色体之间的平衡关系，也就是X\A的比率关系： • 一、当X\A=0.5时，为雄性 • 二、当X\A的比率=1时，为雌性 • 三、当X\A的比率介于0.5与1之间时，表现为间性

  15. Section 5 Dosage compensation effect 1. Barr bodyrefers to an inactivated X chromosome, which is also called sex chromatin body 2.Dosage compensation effect： If one of the two X chromosomes is inactive in the cells of females, the dosage of genetic information that can be expressed in males and females is equivalent 3. Lyon hypothesis 4. Molecular mechanism of random X inactivation

  16. 第五节 剂量补偿效应 • 一 、Barr小体：一种与性别和X 染色体数目有关的异染色质化的小体，它存在于雌性细胞间期核 • 二、 剂量补偿效应：在XY性别决定机制的生物中，使性连锁基因在两种性别中有相等或近乎相等的有效剂量的遗传效应 • 三 、Lyon假说 • 四 、X染色体随机失活的分子机制

  17. Barr Bodies in various human karyotypes

  18. The mechanism of inactivation

  19. Section 6 Crossing over and recombination of linkage gene Linkage versus independent assortment

  20. The relationships between the three genetic laws The law of separation is the basis of the independent assortment law and the law of linkage and crossing over, which lead to a wide variety of genetic variations in the organisms For the independent assortment law and the law of linkage and crossing over, there existed the difference in the transmission of genetic recombination. The genetic recombinations in the former result from the different chromosomes and that in the latter from the homologue Their genetic variations are limited by the length and number of chromosomes, respectively

  21. 三大定律的关系 • 分离律是自由组合律和连锁定律的基础，而后者是生物体遗传的性状发生变异的主流；自由组合与连锁交换二者的差别在于前者是由不同源的染色体所传递，重组类型是由染色体间重组造成，而后者则是由同一对同源染色体所传递的，是染色体内重组所产生的，自由组合受生物染色体对数的限制，而连锁交换则受到其染色体长度的限制

  22. Linkage inheritance Linkage inheritance: is the tendency of genes located in the same chromosome to be associated in inheritance. Linked genes have their loci along the same chromosome, do not assort independently, but can be separated by crossing over. Complete linkage produces only parental or non-crossover gametes. Incomplete linkage produces this exchanged gamete, called recombinant or crossover gametes

  23. Cytological evidence of cross-over

  24. Genetic mechanism of linkage and cross-over

  25. Crossovers and recombinations Single crossovers 单交换 Multiple crossovers 多交换

  26. Linkage and exchange基因间的连锁与交换 完全连锁

  27. Linkage and exchange基因间的连锁与交换 不完全连锁

  28. Cross experiment of two pairs of contrasting traits of pea香豌豆的杂交试验 Flower color: purple (P) dominant versus red (p) recessive Pollen grain shape: long (L) dominant versus round (l) recessive

  29. Purple and long (PPLL)×red and round (ppll) • Results： • Phenotypes of F1 are dominant，four phenotypes of F2; • The ratio of four phenotype of F2is different of classic ratio of 9:3:3:1，two parental phenotypes are higher than theory number，and two combined phenotypes are less than theory number

  30. Purple and round (PPll)×red and long (ppLL)

  31. Purple and round (PPll)×red and long (ppLL) • Results： • Phenotypes of F1 are dominant，four phenotypes of F2; • The ratio of four phenotype of F2is different of classic ratio of 9:3:3:1，two parental phenotypes are higher than theory number，and two combined phenotypes are less than theory number

  32. Coupling phase and repulsion phase Coupling phase: Allelic arrangement in which mutant are on the same chromosome and wild-type alleles are on the homologue Repulsion phase: allelic arrangement in which each homologous chromosome has mutant and wild-type alleles coupling phase versus repulsion phase 相引相：两个显性性状（基因）或两个隐性性状（基因）连在一起遗传 相斥相：一个显性性状（基因）和一个隐性性状（基因）连在一起遗传

  33. The separation law is fit to the allelic gene in the two experiment

  34. Crossing-over Value（交换值） Cross-over value，called recombined ratio，refer to the percent of recombined gametes. The formula is： 亲本型配子+重组型配子 What are method used to test the number of recombined gametes？ Test cross and self-crossing

  35. Linkage and cross-over between C-Sh

  36. Cross over value between P-L(1) • Given the ratio of four gamete produced by F1 PL, Pl*, pL*, and pl is a, b, c, and d respectively; Then： • a+b+c+d=1 • a=d, b=c

  37. Cross over value between P-L(2) • Four phenotypes of nine genotype of F2 are： • P_L_ (PPLL, PPLl, PpLL, PpLl)： a2+2ab+2ac+2bc+2ad • P_ll (PPll, Ppll) ： b2+2bd • ppL_ (ppLL, ppLl) ： c2+2cd • ppll ： d2 The recessive homogenous individuals (ppll) number of F2 may gains from observation (1338)，its ratio is (1338/6952)

  38. The relationship between cross-over value, distance between genes, linkage strength, and genetic distance

  39. Gene location/localization/mapping基因定位与染色体作图 • Gene location/localization：refer to determine location and sequence of genes on chromosome. • Related distance of linked genes may be determined on the basis of cross-over value between two gene, and the sequence may not. • For example： • Maize color C/colorless c, and round Sh/wrinkled sh are on chromosome 9；and the cross-over value between C-Sh is 3.6%. • Hence, there are three or more than three pairs of gene involved in gene locating Linkage groups is a group of gene that have their loci on the same chromosome. In a species, there are as many linkage groups as there are homologous pairs of chromosome or as the haploid number of chromosomes

  40. Mapping（染色体图） Sturtevan and mapping

  41. Sequence of two pair of genes The cross-over value between C-Sh is 3.6 units； Then, there are two possible sequences of them

  42. Two-point test (1)两点测验 • Three crosses between three pairs of gene • For example: there are three pairs of linked genes on chromosome 9. • Grain color： color (C) dominant versus colorless c recessive； • shape：round Sh dominant versus wrinkled sh recessive； • Starch：non-sticky Wx dominant versus sticky wx recessive. • (1) (CCShSh×ccshsh) F1 × ccshsh • (2) (wxwxShSh×WxWxshsh) F1 × wxwxshsh • (3) (WxWxCC×wxwxcc) F1 × wxwxcc

  43. Results of two points test

  44. Two points test (2) Estimate three cross-over values

  45. Two points test (3) Determine distance and related location of between genes. C-Sh: 3.6 Wx-Sh: 20 Wx-C: 22

  46. Three points test (1/7-2/7) 1. Cross： P: wrinkled, non-sticky, color × round, sticky, colorless shsh ++ ++ ++ wxwx cc ↓ F1and test cross: round, non-sticky, color × wrinkled, sticky, colorless +sh +wx +c shsh wxwx cc ↓ 2. Observe traits and class How many phenotypes of F2 , if incomplete linkage？

  47. Three points test(3/7-4/7) 3. Group and count； 4. Determine parental and two-cross over gamete；

  48. Three points test(5/7) 5. Determine the related location Compare parental gametes with two-cross over gametes：The different allele located between two same genes For example：to compare + wx c and sh wx c show only sh is distinct，hence, sh locate between wx and c； Likewise，comparsion sh + + and + + + show that only sh locus is distinct，this also suggest sh locate between wx and c

  49. Determine

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