文本课件遗传学to mendels laws

1、Chapter 3 Extensions to Mendel s Laws Copyright ? The McGraw-Hill Companies, Inc. Permission required to reproduce or display 1 Outline of Chapter 3 Single - gene inheritance in which ? pairs of alleles show deviations from complete dominance ? and recessiveness . different forms of the gene are not

2、 limited to two alleles. ? one gene may determine more than one trait. ? Multifactorial inheritance in which the phenotype ? arises from the interaction of one or more genes with the environment, chance, and each other. Copyright ? The McGraw-Hill Companies, Inc. Permission required to reproduce or

3、display 3-2 Mendelian pattern of inheritance Single - gene trait ? Two alleles ? Clear - cut dominance and recessiveness ? Genotypic ratio 1: 2: 1 ? Phenotypic ratio 3: 1 ? Copyright ? The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-3 Exceptions to Mendelian pattern of

4、inheritance Single - gene trait ? Pairs of alleles show deviations from complete ? dominance and recessiveness . ? Different forms of the gene are not limited to two alleles. ? One gene may determine more than one trait. Multifactorial trait ? Phenotype arises from the interaction of one or ? more g

5、enes with the environment, chance, and each other. Copyright ? The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-4 Dominance is not always complete Crosses between true - breeding strains can produce hybrids with phenotypes different from both parents. plete dominance ? F

6、1 hybrids express an intermediate phenotype that ? differs from both parents. Neither allele is dominant or recessive to the other. ? Phenotypic ratios are the same as genotypic ratios. Codominance ? F1 hybrids express the traits of both parents. ? ? Phenotypic ratios are the same as genotypic ratio

7、s. Copyright ? The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-5 plete dominance in snapdragons Fig. 3.3 Copyright ? The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-6 Codominant lentil coat patterns Fig. 3.4a Copyright ? The McGraw-Hill Com

8、panies, Inc. Permission required to reproduce or display 3-7 Codominant blood group alleles Fig. 3.4b Copyright ? The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-8 Summary of dominance relationships Copyright ? The McGraw-Hill Companies, Inc. Permission required to repr

9、oduce or display 3-9 Fig. 3.2 Do variations on dominance relations negate Mendel s law of segregation? Mendel s law of segregation still applies. ? Dominance relations do not affect the segregation of ? alleles. Dominance relations only affect phenotype. ? Gene products control expression of phenoty

10、pes differently. ? Copyright ? The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-10 A gene may have more than two alleles Genes may have multiple alleles in a population. ? Each individual carries only two of the alternative alleles. ? ? ABO blood group ? 3 alleles: I A ,

11、 I B , and i ? 6 possible ABO genotypes Dominance or recessiveness is always relative to a second allele. ? ? ABO blood group ? I A is completely dominant to i but codominant to I B ? 6 genotypes generate 4 phenotypes Copyright ? The McGraw-Hill Companies, Inc. Permission required to reproduce or di

12、splay 3-11 A paternity lawsuit in 1944: Joan Barry Charlie Chaplin (A type) (O type) A baby girl (B type) Charlie Chaplin (1889-1977) Copyright ? The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-12 How do we establish dominance relations between multiple alleles? Perform

13、 reciprocal ? crosses between pure breeding lines of all phenotypes Dominance series ? Fig. 3.6 Copyright ? The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-13 Mutations are the source of new alleles Multiple alleles arise spontaneously in nature due to ? chance alterati

14、ons in genetic material mutations. Mutation rate varies from 1 in 10,000 to 1 in 1,000,000 ? per gamete per generation. Allele frequency is the percentage of the total number ? of gene copies represented by one allele. Wild - type allele allele whose frequency is more than 1%. ? Mutant allele allele

15、 whose frequency is less than 1%. ? Monomorphic gene with only one wild - type allele. ? Polymorphic gene with more than one wild - type allele. ? Copyright ? The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-14 The mouse agouti gene: One wild - type allele, many mutant a

16、lleles ( 14) Copyright ? The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-15 Fig. 3.7a-b Copyright ? The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-16 Fig. 3.7c One gene may contribute to several visible characteristics Pleiotropy A single

17、gene determines a number of ? distinct and seemingly unrelated characteristics. One recessive mutation in Maori people causes respiratory ? problems and infertility in men. Copyright ? The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-17 Some alleles affect viability. ? A

18、lleles that affect viability ? often produce deviations from a 1:2:1 genotypic and 3:1 phenotypic ratio. Fig. 3.9 Copyright ? The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-18 A dominant coat color allele also produces recessive lethality in mice A Y is dominant to A i

19、n ? determining coat color. Yellow must be A Y A. ? A Y is recessive to A in ? producing viability. Yellow mice do not breed ? true. A Y A Y die in utero and do ? not show up as progeny. Fig. 3.9 Copyright ? The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-19 Copyright ?

20、 The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-20 Sickle - cell syndrome Multiple alleles ? Wild - type is Hb ? A ? More than 400 mutant alleles identified so far ? Hb ? S allele specifies abnormal peptide causing sickling ? among red blood cells Pleiotropy ? Hb ? S a

21、ffects more than one trait ? Muscle cramps, shortness of breath, and fatigue ? Anemia ? Resistance to malaria ? Recessive lethality ? Homozygous Hb ? S Hb ? S individuals die at young age. ? Different dominance relations ? Heterozygous Hb ? A Hb ? S individuals e sick in ? low - oxygen environment.

22、Copyright ? The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-21 Pleiotropy of sickle - cell syndrome Copyright ? The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-22 Fig. 3.10 Multifactorial inheritance Novel phenotypes can emerge from the com

23、bined ? action of the alleles of two genes. Copyright ? The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-23 Two genes, A and B, ? interact to produce new colors in lentils. AABB , AABb , AaBB , ? and AaBb are brown. AAbb and Aabb are ? tan. aaBB and aaBb are ? gray. aabb

24、 is green and ? breeds pure. Fig. 3.11a Copyright ? The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-24 Complementary gene action generates flower color in sweet - peas 9:7 (purple: white) ratio demonstrates that one dominant allele of two genes must be present to produc

25、e purple flowers Copyright ? The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-25 Fig. 3.12 Two genes work in tandem to produce purple pigment Fig. 3.13 Copyright ? The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-26 Epistasis , the effects of

26、 one gene s alleles mask the effects of another gene s alleles Recessive epistasis ? The recessive allele of ? one gene hides the effects of another gene. Dominant epistasis ? The dominant allele of ? one gene hides the effects of another gene. Copyright ? The McGraw-Hill Companies, Inc. Permission

27、required to reproduce or display 3-27 Recessive epistasis : Coat color in Labrador retrievers Fig. 3.14a Copyright ? The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-28 Recessive epistasis in human blood groups Bombay phenotype mutant recessive allele at second gene hh m

28、asks phenotype of ABO alleles. Woman Man (O type) (O type) Children (A or B type) Fig. 3.14b Copyright ? The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-29 Dominant epistasis in summer squash Fig. 3.15a Copyright ? The McGraw-Hill Companies, Inc. Permission required to

29、reproduce or display 3-30 Several genes can contribute to the same trait Heterogeneous traits are traits determined by a ? number of different genes. A mutation at any one of these genes can give rise to the same phenotype. Albinism in plants, animals and humans. ? Deafness in humans is a heterogene

30、ous trait. ? About 50 different genes have mutant alleles that can cause deafness. Copyright ? The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-31 Difficult to determine which of many genes mutated in ? a person with a heterogeneous mutant phenotype. Complementation test

31、ing can determine if mutations ? arise from the same or different genes. Fig. 3.16 Copyright ? The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-32 Breeding studies help determine how a trait is inherited How do we know if a trait is caused by one ? gene or two genes that

32、 interact? Ratios such as 9:7 or 13:3 can indicate potential ? gene interaction. ? Further breeding studies can confirm hypotheses. Copyright ? The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-33 Testing two gene and one gene hypothesis example from mice Fig. 3.18a Copyr

33、ight ? The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-34 Fig. 3.18b Copyright ? The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-35 Summary of genetic variations on multifactorial traits Genes can interact to generate new phenotypes. ? The

34、dominant alleles of two interacting genes ? can both be necessary for producing a phenotype. One gene s alleles can mask the effects of ? another gene s. Mutants alleles at one of two or more different ? genes can result in the same phenotype. Copyright ? The McGraw-Hill Companies, Inc. Permission r

35、equired to reproduce or display 3-36 Copyright ? The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-37 The same genotype does not always produce the same phenotype Phenotype often depends on penetrance and ? expressivity. Penetrance percentage of individuals with a ? parti

36、cular genotype that show the expected phenotype in a population. ? Penetrance can be complete (100%) or plete (retinoblastoma 75%). Expressivity degree or intensity with which a ? particular genotype is expressed in a phenotype Expressivity can be variable or unvarying. ? Copyright ? The McGraw-Hill

37、 Companies, Inc. Permission required to reproduce or display 3-38 Modifier genes have subtle, secondary effect on a ? phenotype from a major gene. Environment can affect the phenotypic expression of a ? genotype. Temperature ? Coat color in Siamese cats is lighter in its extremities. ? Conditional lethals ? shibire gene in fly is lethal at temperatures above 29 o C. ? Phenocopy chan