内蒙古大学遗传学双语教学课件.ppt

chapter 3,mendelian genetics,inherited characteristics are under the control of particulate factors called genes that are transmitted from generation to generation on vehicles call chromosomes, according to rules first described by gregor mendel. the outcomes of crosses subject to these rules are affected by chance deviation and may be evaluated using statistical analysis.,3.1 the hybrid experiment before mendel,1. knight,in 1797, knight (british) crossbreed gray garden pea with white garden pea,but he did not calculate the number!,f1,f1,parents, p,first filial, f1,second filial, f2,2. nauding,in 1863，nauding（france）published a paper about plant hybrid cross,（1）reciprocal crosses with the same results,（2）during the formation of gametes，the factors which control the traits must go to different gametes.,这已经先于mendel两年意识到了性状的分离本质。,otherwise one could not explain the f2 ！,3.2 mendels experiments,in 1856, mendel performed his first set of hybridization experiment with the garden pea. he reported the results in 1865.,1. the monohybrid cross,（1）traits（性状）,seven visible features; each represented by two contrasting forms.,（2）results of the monohybrid cross,（3）characters of the results, all f1 offspring were identical to one of the parents., but in f2 offspring, an approximate ratio of 3:1 was obtained., not sex-dependent., looked like the f1, while is the contrasting trait which disappeared in the f1 generation.,reciprocal cross had the same results.,p,f1,f2,parents, p,first filial, f1,second filial, f2,f2,p,3,1,dominance: trait appears in all of the f1,recessiveness: disappears in f1 but reappears in f2,（4）explain the results,mendels first three postulates：, unit factors in pairs,genetic characters are controlled by unit factors that exist in pairs in individual organisms., dominance/recessiveness,when two unlike unit factors responsible for a single character are present in a single individual, one unit factor is dominant to the other，which is said to be recessive., segregation,during the formation of gametes, the paired unit factors separate or segregate randomly so that each gamete receives one or the other with equal likelihood.,gametes,the physical appearance of a trait .,phenotype（表现型）:,gene：,mendels unit factor represent units of inheritance.,modern genetic terminology,we use the first letter (italic) of the recessive trait to symbolize the gene.,（tall，white，round),alternative forms of a single gene called alleles.,alleles（等位基因）,d (dwarf): height of the pea.,w (white): color of pea flower.,d : dwarf pea.,w : white flower.,d : tall pea.,height,recessive gene.,dominant gene.,w : purple flower.,recessive gene.,dominant gene.,color,genotype（基因型）,genotype（基因型）,the two unit factors present in any individual（dd, dd, or dd），these symbols are called the genotype.,homozygote（纯合子）,when both alleles are the same (dd or dd), the individual is said to be homozygous or a homozygote.,heterozygote（杂合子）,when the alleles are different (dd), we use the term heterozygous or heterozygote.,explain pea inheritance,tall: about 2m.,dwarf: about 0.2m.,monohybrid,predicted ratios,（5）test cross,heterozygous f1 cross with homozygous recessive.,the focus: what is the genotype of f1 ?,dd,dd,both should be tall pea!,or,method: cross f1 with dd（dwarf pea）.,test cross results,if f1 is dd,57,53,48,48,正交,反交,if f1 is dd,test cross results,（6）后人对mendel杂交实验的重复结果,2. the dihybrid cross,（1）traits（example）,to examine two characters simultaneously., seed shape:, seed color:,round : dominant wrinkled: recessive,yellow : dominant green: recessive,（2）results,12/16,4/16,12/16,4/16,3:1,9:3:3:1,（3）explain the results,f2 results of dihybrid could be predicted as two monohybrids occur independently.,9:3:3:1,（3:1） （3:1）=,during gamete formation, segregating pairs of unit factors assort independently of each other.,mendels fourth postulate：,independent assortment（自由组合）：,two traits inherit independently,color and shape genes do not mix !,calculate f2 ratios,9,3,3,1,f1 gametes combine independently,（4）test cross,heterozygous f1 cross with homozygous recessive., the focus: how f1 produces gametes?,g and w（g and w）separate independently to form:,gw,gw,gw,gw,or,g and w（g and w）transfer together as they in parents:,gw,gw,gw,gw,or,4 kinds,2 kinds, results of test cross,3. multiple traits cross,（1）trihybrid cross:,three traits.,23=8,8 kinds,calculate f2 ratios：by probability（概率）,(3:1)(3:1) (3:1)=27:9:9:9:3:3:3:1,（2） multiple traits ：n pairs of genes,f1 produces 2n kinds of gametes！,tetrahybrid cross!,3.3 genes and homologous chromosomes,the independent assortment is behavior of homologous chromosome in meiosis.,1. precondition:,alleles locate on different homologous chromosomes.,a,a,b,b,c,c,d,d,during meiosis，they will separate along with the homologous chromosome.,2. monohybrid cross,a a,a a,a：dominant a: recessive,p,f1,gametes,f2,genotypes,phenotypes,genotypes,3. dihybrid cross,two pairs of alleles locate on two pairs of homologous chromosome.,g,g,w,w,g,g,w,w,during meiosis，they will separate along with the homologous chromosome.,g,g,w,w,after replication,a,a,b,b,a,a,b,b,f1,3.4 chi-square（ 2 ） analysis,to evaluate the influence of chance on genetic data.,1. the preconditions for mendels ratios,（1）each allele is dominant or recessive.,（2）segregation is operative,（3）independent assortment occurs,（4）fertilization is random,（5）all offspring survive equally,2. goodness of fit（适合度，好适度）,（1）chance deviation（机会偏差）,deviation was induced by chance., toss coin,toss 1000,head and tail each 500,predict,head 486 ; tail 514,observed,并非必然事件或人为主观故意引起。,投掷次数越多，越接近概率预期（机会偏差越小）。,deviation：observation prediction, take go out of bag,1000 times,black and white 500,predict,black 486， white 514,observe,（2） how to reduce the deviation,as the sample size increase, the average deviation from the expected results decrease.,抓的次数越多，越接近于黑白各半（机会偏差越小）。,3：1,（1）expectation：,9：3：3：1,or,（2）observation,2.9：1,9.1：3.1：2.9：1,or,maybe,3. chance deviation in mendels experiments,observation,expectation,?,2.9 ：1,3.0 ：1,（3）goodness of fit,only if the deviation is purely of chance！,so we must prove that our deviation is indeed induced by chance.,we just need to show the probability of chance deviation.,deviation（difference） always exists.,2（chi-square） analysis：,2 is used to represent deviation degree.,2=,(oe)2,e,o：observed（观察值） e： expected（预期值） d： deviation（偏差）,or,2=,d2,e,4. statistical （统计学的）method,d = o e,（1）calculate 2 value,（2）interpret the 2 value,so 2 value must be changed to p value（probability）.,换算方法复杂，一般直接查现成的2表。,查2表注意事项：,df : degree of freedom（自由度）：,df = n1,n: