内蒙古大学遗传学双语教学课件

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1、Mendelian GeneticsInherited 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 c

2、hance deviation and may be evaluated using statistical analysis. 1. KnightIn 1797, Knight (British) crossbreed gray garden pea with white garden peaBut he did not calculate the number!F1F1Parents, PFirst filial, F1Second filial, F22. NaudingIn 1863，Nauding（France）published a paper about plant hybrid

3、 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. 这已经先于这已经先于Mendel两年意识到了性状的分离两年意识到了性状的分离本质。本质。Otherwise one could not explain the F2 ！3.2 Mendels ExperimentsIn 1856, Mendel performed his first set of

4、 hybridization experiment with the garden pea. He reported the results in 1865.1. The Monohybrid Cross（1）Traits（性状性状）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.

5、 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.PF1F2Parents, PFirst filial, F1Second filial, F2F2P31Dominance: Trait appears in all of t

6、he F1Recessiveness: Disappears in F1 but reappears in F2（4）Explain the ResultsMendels First Three Postulates： Unit factors in pairsGenetic characters are controlled by unit factors that exist in pairs in individual organisms. Dominance/RecessivenessWhen two unlike unit factors responsible for a sing

7、le character are present in a single individual, one unit factor is dominant to the other，which is said to be recessive. SegregationDuring the formation of gametes, the paired unit factors separate or segregate randomly so that each gamete receives one or the other with equal likelihood.gametesThe p

8、hysical appearance of a trait .Phenotype（表现型表现型）: Gene：Mendels unit factor represent units of inheritance.Modern Genetic TerminologyWe 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（等位基因等位基因）d (d

9、warf): height of the pea.w (white): color of pea flower.d : dwarf pea.w : white flower.D : tall pea.HeightRecessive gene.Dominant gene.W : purple flower.Recessive gene.Dominant gene.ColorGenotype（基因型基因型）Genotype（基因型基因型）The two unit factors present in any individual（DD, Dd, or dd），these symbols are c

10、alled the genotype.Homozygote（纯合子纯合子）When both alleles are the same (DD or dd), the individual is said to be homozygous or a homozygote.Heterozygote（杂合子杂合子）When the alleles are different (Dd), we use the term heterozygous or heterozygote.Explain Pea InheritanceTall: about 2m.Dwarf: about 0.2m.Monohy

11、bridPredicted ratios（5）Test CrossHeterozygous F1 cross with homozygous recessive.The focus: what is the genotype of F1 ?DDDdBoth should be tall pea!orMethod: cross F1 with dd（dwarf pea）.Test Cross resultsIf F1 is DD57534848正交正交反交反交If F1 is DdTest Cross results（6）后人对）后人对Mendel杂交实验的重复结果杂交实验的重复结果2. The

12、 Dihybrid Cross（1）Traits（example）To examine two characters simultaneously. Seed shape: Seed color:round : dominantwrinkled: recessiveyellow : dominantgreen: recessive（2）Results12/164/1612/164/163:19:3:3:1（3）Explain the resultsF2 results of dihybrid could be predicted as two monohybrids occur indepen

13、dently.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（自由组合自由组合）：）：Two traits inherit independentlyColor and shape genes do not mix !Calculate F2 ratios9331F1 gametes combine independentl

14、y（4）Test crossHeterozygous F1 cross with homozygous recessive. The focus: how F1 produces gametes?G and W（g and w）separate independently to form:GWGwgWgwor G and W（g and w）transfer together as they in parents:GWgwGwgWor4 kinds2 kinds Results of Test Cross3. Multiple Traits Cross（1）Trihybrid cross:th

15、ree traits.23=88 kindsCalculate F2 ratios：by probability（概率概率）(3:1)(3:1) (3:1)=27:9:9:9:3:3:3:1（2） Multiple Traits ：n pairs of genesF1 produces 2n kinds of gametes！3.3 Genes and Homologous ChromosomesThe independent assortment is behavior of homologous chromosome in meiosis.1. Precondition:Alleles l

16、ocate on different homologous chromosomes.AaBbCcDdDuring meiosis，they will separate along with the homologous chromosome.2. Monohybrid CrossA Aa aA：dominanta: recessivePF1gametesF2genotypesphenotypesgenotypes3. Dihybrid CrossTwo pairs of alleles locate on two pairs of homologous chromosome.GGWWggwwD

17、uring meiosis，they will separate along with the homologous chromosome.GgWwAfter replicationAaBbAaBbF13.4 Chi-Square（ 2 ） AnalysisTo 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）Independen

18、t assortment occurs（4）Fertilization is random（5）All offspring survive equally2. Goodness of Fit（适合度，好适度适合度，好适度）（1）Chance Deviation（机会偏差机会偏差）Deviation was induced by chance. Toss coinToss 1000Head and tail each 500predictHead 486 ; tail 514observed并非必然事件或人为主观故意引起。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

19、）。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 bag1000 timesBlack and white 500predictBlack 486， white 514observe（2） How to reduce the deviationAs the sample size increase, the average deviation from the expected results decrease.抓的次数越多，越接近于黑白各半抓的次数越多，越接近于黑白各半（机会偏差越小）。（机会偏差

20、越小）。3：1（1）Expectation：9：3：3：1or（2）Observation2.9：19.1：3.1：2.9：1ormaybe3. Chance Deviation in Mendels ExperimentsObservationExpectation?2.9 ：13.0 ：1（3）Goodness of FitOnly 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 pro

21、bability of chance deviation.Deviation（difference） always exists. 2（Chi-square） analysis： 2 is used to represent deviation degree. 2=(OE)2EO：Observed（观察值观察值）E： Expected（预期值预期值）D： Deviation（偏差偏差） or 2=D2E4. Statistical （统计学的统计学的）MethodD = O E（1）Calculate 2 value （2）Interpret the 2 valueSo 2 value mus

22、t be changed to p value（probability）.换算方法复杂，一般直接查现成的换算方法复杂，一般直接查现成的 2 2表。表。查查 2 2表注意事项：表注意事项：df : degree of freedom（自由度自由度）：）：df = n1n: categories(实验结果中所涉及的项目实验结果中所涉及的项目）How much is the chance probability of this 2 value？Effect of df on p of 2The more is df, the big is p (with the same 2)。Standard 2

23、 tablep（3）Assess the p valueCriterion of assessment：p = 0.05 If p0.05More than 5% of deviation is because of chance.If p0.05Less than 5% of deviation is because of chance.Observed = Expected Observed Expected 3.5 2 Analysis of Mendels Hybrid Results 21. Monohybriddf=1(2-1)（1）Calculate 2 value（2） Look up 2 table0.20p 0.05，Observed ratio is expected ratio.When： 20.461.64）；）；df=12. Dihybriddf =4-1=3 2=0.71+0.34+2.33+0.78=4.160.20p0.05，Observed ratio is expected ratio.