微生物遗传.ppt

1、Microbial Genetics and Breeding,Part 2: Fungal Genetics A) Classic genetics of fungi B) Molecular genetics of fungi,Genetics,Genetics is the study of heredity and variation, that is genotype Vs phenotype,Heredity （遗传）is the phenomenon whereby biological traits are transmitted from one generation to

2、another.,Trait,A phenotypic trait is an obvious and observable trait; it is the expression of genes in an observable way. An example of a phenotypic trait is hair color, there are underlying（根本的） genes that control the hair color, which make up the genotype, but the actual hair color, the part we se

3、e, is the phenotype. The phenotype is the physical characteristics（体格特征） of the organism. The phenotype is controlled by the genetic make-up of the organism and the environmental pressures the organism is subject to. （使遭受）,A trait may be any single feature or quantifiable measurement of an organism.

4、 However, the most useful traits for genetic analysis are present in different forms in different individuals. A visible trait is the final product of many molecular and biochemical processes. In most cases, information starts with DNA traveling to RNA and finally to protein (ultimately affecting or

5、ganism structure and function). This is the central dogma（中心法则） of molecular biology as stated by Francis Crick,More on Trait,Genetic Analysis,Phenotype Vs Genotype,Forward Genetics,Phenotype (Mutant),Genotype,Reverse Genetics 反向遗传学,Genotype,Phenotype,Genetic Analysis: Genotype Vs Phenotype,Allele:

6、（等位基因 ）Alternate forms of a gene/factor Genotype: Combination of alleles an organism has Phenotype: How an organism appears,Why Genetic Analysis ?,优质突变株的诱变和筛选,Haploid（单倍体） MATa（甲硫氨酸S-腺苷基转移酶）strain,Screening筛选for mutants with the desirable trait,UV,ethylmethanesulfonate 乙基甲磺酸, Mutants can be isolated

7、 and characterized without any a priori （以前的）understanding of the molecular basis of the function. To determine how many genes are involved in a function? To find other genes whose products may interact（互相影响, 交互作用）either physically（身体上）or functionally with the products of these genes.,Major advantag

8、es of classical genetic approach,1) Isolation of mutants Dominance-recessiveness (显性-隐性)test 3) Complementation test互补测验（Recombination test重组实验） Epistatic-hypostatic test上位性-下位性 5) Linkage analysis,Five main genetic approaches,Vocabulary,Allele:等位基因, Alternate forms of a gene/factor. Genotype: combi

9、nation of alleles an organism has. Phenotype: How an organism appears. Dominant显性的: An allele which is expressed (masks the other). Recessive:隐性An allele which is present but remains unexpressed (masked) Homozygous:纯合子Both alleles for a trait are the same. Heterozygous:杂合子The organisms alleles for a

10、 trait are different.,Mendel: the Farther of Modern Genetics,Mendel observed that organisms inherit traits via discrete（分离）units of inheritance遗传, which are now called genes., Born Johann Mendel孟德尔in 1822 Took name of Gregor孟德尔 as a monk（道名） Mendel was a member of a monastery修道院in what is now the Cz

11、ech Republic（捷克共和国） Studied physics and botany植物学in the University of Vienna维也纳(1851-1853) Began first hybridization杂交experiments on the garden pea豌豆in 1856 Research ended in 1868 when promoted to abbot (修道院院长),Mendel,Blending Inheritance 混合遗传,Many biologists and other academics held to坚持the idea of

12、 blending inheritance混合遗传during the 19th century, prior to the discovery of genetics遗传学. Blending inheritance混合遗传was merely a widespread hypothetical假说的,假设的,假定的model, in which it was thought inherited traits遗传性状were determined, randomly随机地,任意地, from a range bounded限于(受约束)by the homologous同源的traitsfo

13、und in the parents双亲.,Inheritance of acquired characteristics,The inheritance of acquired characteristics（获得性状遗传）is a hypothesis（假设,假说）that physiological生理学的changes acquired over the life of an organism (such as the enlargement of a muscle through repeated use) may be transmitted to offspring（后代）. I

14、t is also commonly referred to（提到; 说起）as the theory of adaptation适应equated（使相等, 视为平等, 等同with the 0evolutionary theory（进化论）of French naturalist Jean-Baptiste Lamarck known as Lamarckism.（ 拉马克学说),Through the selective cross-breeding of 28,000+ common pea plants over many generations between 1856 and 1

15、863), Mendel discovered that certain traits show up in offspring(后代）without any blending of parent characteristics. For instance, the pea flowers are either purple紫色的or white. Intermediate中间的colors do not appear in the offspring of cross-pollinated交叉的;传粉,授粉pea plants. Mendel observed seven traits th

16、at are easily recognized and apparently only occur in one of two forms:,1. Flower color is purple or white 2. Flower position is axil枝腋下 or terminal（末端） 3. Stem length is long or short 4. Seed shape is round or wrinkled皱 5. Seed color is yellow or green 6. Pod豆荚shape is inflated膨大的,膨胀的or constricted

17、缩小的 7. Pod color is yellow or green,The theories of heredity attributed to Gregor Mendel, based on his work with pea plants, are well known to students of biology. But his work was so brilliant and unprecedented空前的，史无前例的at the time it appeared that it took thirty-four years for the rest of the scien

18、tific community科学共同体to catch up to it. The short monograph, Experiments with Plant Hybrids, in which Mendel described how traits were inherited, has become one of the most enduring持久的and influential 有影响的publications出版物in the history of science.,Mendels Contributions to Genetics,Law of segregation (分

19、离规律） Law of independent assortment (独立分配） Dominance or recessiveness of gene (基因显隐性）,Mitosis (有丝分裂）,The number of chromosomes per cell is maintained,Meiosis （减数分裂）,The number of chromosomes per cell is cut in half,Allele,Dominance or Recessiveness of Gene,Law of Segregation 分离定律,When gametes配子(sperm

20、精子egg etc) are formed each gamete will receive one allele or the other,A,A,a,A,a,Gamete formation,a,A,Law of Independent Assortment 独立分配定律,During gamete formation, segregating pairs of unit factors assort（分配） independently of each other,A,a,B,b,A,B,A,b,a,b,a,B,Mendels Work “Forgotten” Initiated开始,着手

21、in 1856, presented提出in 1865, published出版 1866 Mathematical analyses数学分析in genetics quite unusual Did not fit other ideas about genetics Darwin/Wallace ideas preferred优先的 continuous variation连续变异(not “discontinuous variation”) Rediscovered and significance appreciate赏识34 years later,Rediscover of Men

22、dels Work,Karl Correns,Hugo de Vires,Erich Tschermak,The Discovery of Gene Linkage基因连锁,Bateson, Punnett,P P L L (purple, long) X p p l l (red, round),P p L l (Self),F1,Number of Progeny Phenotype (and genotype) Observed Expected from 9:3:3:1 Purple, long (P _ L _) 284 215 Purple, round (P _ l l) 21

23、71 Red, long (p p L _) 21 71 Red, round (p p ll) 55 24 Total 381 381,Autosome（常染色体）Gene Linkage基因连锁and Crossing over交换,pr, purple eye Pr+, red eye,vg, vestigial wing残翅 vg+, normal wing,pr+ vg+,pr vg,X,pr+ vg+ 1339 pr vg 1195 pr+ vg 151 pr vg+ 154 2839,pr,pr+,vg,vg+,pr,pr+,vg,vg+,Expected ratio,1,1,1

24、,1,Recombinant frequency = 重组频率,151+154,2839,X 100%,= 10.7%,Autosome 常染色体,摩尔根的染色体理论及连锁互换定律,1. 根据果蝇伴性遗传现象提出基因位于染色体上的假说 2.发现位于同一染色体上的基因之间的连锁、交换，建立了遗传学的第三定律连锁交换定律,Morgans Chromosome Theory of Heredity 染色体遗传学说,Based on the discovery of sex-linked inheritance（伴性遗传） of white eye,In 1910, T. H. Morgan disc

25、overed a white-eyed mutation with unusual “sex-linked” inheritance,Sex linkage of white-eyed mutant (w) was important proof that genes were on chromosomes.,Sex-linked inheritance 伴性遗传,Morgan observed that the gene for eye colour is linked to the X chromosome,The case of the white-eyed mutant,Wild ty

26、pe (red-eyed) male,Mutagen 诱变剂,White-eyed male,Wild type (red-eyed) female,X,F1 phenotype : All red-eyed,Red eye is dominant显性的to white eye,Hypothesis假设,假说,A cross杂交between the F1 flies苍蝇should give us: red eye : white eye = 3:1,An interesting observation,A reciprocal cross 反交,Morgan tried the cross

27、杂交the other way roundwhite-eyed female x red-eyed male (XwXw X Xw+Y） Result:All red-eyed females and all white-eyed males This confirmed what Morgan suspected The gene for eye colour is linked to the X chromosome,Morgans Hypothesis Diagrammed简图,W is on X chromosome,There is no w+ allele on Y,Tests o

28、f predictions of Morgans Hypothesis,The above observations by Morgan were first direct evidence placing a gene on a specific chromosome.,Evidence that recombination results from reciprocal相互的exchange between homologous chromosomes同源染色体,Recombination frequencies are the basis of genetic map遗传学图,RF: r

29、ecombination frequency; 1% RF= 1 Centimorgan (cM)=1 map unit (m.u.) 厘摩尔根,Mapping genes by comparison of two-point crosses,优质突变株的诱变和筛选,Haploid单倍体MATa strain,Screening筛选for mutants with the desirable trait,UV,ethylmethanesulfonate 乙基甲磺酸,甲硫氨酸S-腺苷基转移酶,目的突变株的诱变, 筛选和鉴定,Haploid MATa strain,Screening for mu

30、tants with the desired trait,UV,ethylmethanesulfonate,For example, if Yfg- (Your Favorite Gene) represents表现an auxotrophic营养缺陷型的requirement, such as arginine精氨酸, or temperature-sensitive mutants （温度敏感突变株）unable to grow at 37 C.,Mitosis (有丝分裂）,The number of chromosomes per cell is maintained,Meiosis

31、（减数分裂）,The number of chromosomes per cell is cut in half,Law of Segregation分离定律,When gametes配偶子(sperm egg etc) are formed each gamete will receive one allele or the other,A,A,a,A,a,Gamete formation,a,A,Law of Independent Assortment 独立分配定律,During gamete formation, segregating pairs of unit factors as

32、sort（分配） independently of each other,A,a,B,b,A,B,A,b,a,b,a,B,摩尔根的染色体理论及连锁互换定律,1. 根据果蝇伴性遗传现象提出基因位于染色体上的假说 2.发现位于同一染色体上的基因之间的连锁、交换，建立了遗传学的第三定律连锁交换定律,Sex-linked inheritance,Morgan observed that the gene for eye colour is linked to the X chromosome,Morgans Hypothesis Diagrammed,W is on X chromosome,Ther

33、e is no w+ allele on Y,Tests of predictions of Morgans Hypothesis,Recombination frequencies are the basis of genetic map,RF: recombination frequency; 1% RF= 1 Centimorgan (cM)=1 map unit (m.u.),Mapping genes by comparison of two-point crosses,Tetrad Analysis in Fungi,Ordered tetrad顺序四分体analysis Unor

34、dered tetrad非顺序四分体analysis,Tetrad 四分体,Adult 2n,Adult 2n,Meiosis n n n n,Meiosis n n n n,2n Zygote,2n Zygote,The diploid二倍体life cycle.,Many Mitosis,Many Mitosis,n Adult,n Adult,Mitosis,Transient diploid meiocyte,Many mitosis,Many mitosis,Meiosis,Representative n cells,Representative n cells,2n,Mitosi

35、s,n n n n,The haploid（二倍体）life cycle生命周期,Ordered tetrad顺序四分体analysis,Using Neurospora crassa (粗糙面包霉) as a model system模式系统,The life cycle生命周期of the bread mold毛霉目的真菌,面包霉Neurospora crassa(链孢霉属),The products of a single meiosis减数分裂are packaged in a sac (ascus),How ordered tetrads顺序四分体form,Arrangement o

36、f the four chromatids染色单体of each homologous chromosome同源染色体pair,The products of a single meiosis减数分裂,1st Division Meiosis,Haploid,Diploid,Ordered Tetrads顺序四分体help locate genes in relation to the centromere着丝粒,怎么知道二个基因是否是连锁的?,亲二型 (PD),非亲二型 (NPD),parental ditype (PD)亲二型：链孢霉等真菌的四分体出现两种基因型，和双亲的基因型相同 non

37、parental-ditype (NPD)非亲二型：含有两种基因型的四分体，而这两种基因型却是重组型。,How do you determine linkage?,You cross AB x ab and find in 100 tetrads: 48 PD (亲二型） 52 NPD （非亲二型） Are A and B linked?,Mendels Law,1. Segregation: Equal numbers of B and b * The phenotype resulting from a mutation in a single gene will segregate ex

38、actly 2B : 2b. Does the phenotype segregate 2:2? Yes. B and b are alleles of a single gene. 2. Independent Assortment独立分配(linkage): AB x ab * Tetrad四分体number: Are PD = NPD ?,Two genes are unlinked,Two genes are linked,Yes,NO,Complete Linkage完全连锁of Two Genes,The Products of a Single Crossover,Parenta

39、l,Recombinant,Recombinant,Parental,Tetratype,2. Independent Assortment (linkage): AB x ab Tetrad number: Are PD = NPD ?,Yes No,2 genes are linked Tetratype (四型）?,Yes NO,100% linked,Map Distance,centiMorgans,=,1/2 T,TOTAL,2 genes are unlinked,T = 四型,连锁图距,How do you determine linkage?,You cross AB x a

40、b and find in 100 tetrads: 90 PD 10 T Are they linked? 90 PD = 90 X4 = 360 Non-Recombinant Progeny 10 T = 10 x 2 = 20 Recombinant Progeny MD in centimorgans = Recombinants/4XTotal tetrads X 100 MD = 20/400 X 100 = 5 centiMorgans,Map Distance centiMorgans,=,1/2 T,TOTAL,X 100,DOUBLE CROSSOVERS双交换,CROSSING OVER OCCURS AT THE 4 STRAND STAGE,ESTIMATION OF DOUBLE CROSSOVERS,Singles = TT Doubles = 1P