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Observing Patterns in Inherited Traits     Chapter 11
Impacts, Issues:The Color of Skin Like most human traits, skin color has a genetic  basis; more than 100 gene products af...
11.1 Mendel, Pea Plants,and Inheritance Patterns Recurring inheritance patterns are observable  outcomes of sexual reprod...
Mendel’s Experimental Approach Mendel was a monk with training in plant  breeding and mathematics He studied the garden ...
Garden Pea Plant:Self Fertilization and Cross-Fertilization
carpel    antherA Garden pea flower, cut in half. Sperm form inpollen grains, which originate in male floral parts(anthers)....
Animation: Crossing garden pea plants
Terms Used in Modern Genetics Genes  • Heritable units of information about traits  • Parents transmit genes to offspring...
Terms Used in Modern Genetics A mutation is a permanent change in a gene   • May cause a trait to change   • Alleles are ...
Terms Used in Modern Genetics An individual with nonidentical alleles of a gene  is heterozygous for that gene An indivi...
Terms Used in Modern Genetics An allele is dominant if its effect masks the  effect of a recessive allele paired with it ...
Terms Used in Modern Genetics Gene expression  • The process by which information in a gene is    converted to a structur...
Terms Used in Modern Genetics Genotype  • The particular alleles an individual carries Phenotype  • An individual’s obse...
Terms Used in Modern Genetics P stands for parents, F for filial (offspring) F1: First generation offspring of parents ...
11.1 Key ConceptsWhere Modern Genetics Started Gregor Mendel gathered the first experimental  evidence of the genetic bas...
11.2 Mendel’s Law of Segregation Garden pea plants inherit two “units” of  information for a trait, one from each parent
Testcrosses Testcross  • A method of determining if an individual is    heterozygous or homozygous dominant  • An individ...
Monohybrid Experiments Monohybrid experiments  • Testcrosses that check for a dominance    relationship between two allel...
Mendel’s Monohybrid Experiments Mendel used monohybrid experiments to find  dominance relationships among pea plant trait...
Segregation of Alleles at a Gene Locus
homozygous                        homozygousdominant parent                  recessive parent               (chromosomes  ...
homozygous                        homozygousdominant parent                  recessive parent               (chromosomes  ...
Mendel’s Monohybrid Experiments
Trait        Dominant    Recessive     F2 Dominant-to-Studied        Form        Form        Recessive RatioSeedshape     ...
Calculating Probabilities Probability  • A measure of the chance that a particular    outcome will occur Punnett square ...
Construction of a Punnett Square
Phenotype Ratiosin a Monohybrid Experiment
Phenotype Ratiosin a Monohybrid Experiment
Fig. 11-7, p. 173
female gametes                      A     a             A      a             A     a              A         amale gametes ...
F1 offspring               aaTrue-breeding homozygousrecessive parent plant                                a      a       ...
F2 offspring               AaHeterozygousF1 offspring                               A     a                               ...
Mendel’s Law of Segregation Mendel observed a phenotype ratio of 3:1 in the  F2 offspring of his monohybrid crosses  • Co...
11.2 Key ConceptsInsights from Monohybrid Experiments Some experiments yielded evidence of gene  segregation: When one ch...
11.3 Mendel’s Lawof Independent Assortment Mendel’s law of independent assortment  • Many genes are sorted into gametes  ...
Dihybrid Experiments Dihybrid experiments  • Tests for dominance relationships between    alleles at two loci  • Individu...
Independent Assortment at Meiosis
One of two possible alignments            The only other possible alignmenta Chromosome                                   ...
One of two possible alignments            The only other possible alignmenta Chromosome                       A   Aa      ...
Mendel’s Dihybrid Experiments
Fig. 11-9a, p. 175
parent plant parent plant                                               homozygous homozygousP                            ...
Fig. 11-9b, p. 175
AaBb   AaBb       AaBbF1           All F1 offspring are AaBb,generation   with purple flowers and tall stems.             ...
Fig. 11-9c, p. 175
AB                   Ab                 aB                 ab    AB     AABB                AABb               AaBB       ...
Animation: Dihybrid cross
Mendel’s Law of IndependentAssortment Mendel’s dihybrid experiments showed that  “units” specifying one trait segregated ...
11.3 Key ConceptsInsights from Dihybrid Experiments Some experiments yielded evidence of  independent assortment: Genes a...
11.4 Beyond Simple Dominance Mendel focused on traits based on clearly  dominant and recessive alleles; however, the  exp...
Codominance in ABO Blood Types Codominance  • Two nonidentical alleles of a gene are both fully    expressed in heterozyg...
Codominance in ABO Blood Types
AA        BB                or        orGenotypes:      AO   AB   BO   OOPhenotypes(Blood type):   A    AB   B    O       ...
Animation: Codominance: ABO bloodtypes
Incomplete Dominance Incomplete dominance  • One allele is not fully dominant over its partner  • The heterozygote’s phen...
Incomplete Dominance in Snapdragons
Fig. 11-11a, p. 176
homozygous    homozygous          heterozygous F1            x parent (rr)parent (RR)                       offspring (Rr)...
Fig. 11-11b, p. 176
R      rB Cross two F1 plants,     Rand the three phenotypes                               RR   Rrof the F2 offspring will...
Epistasis Epistasis  • Two or more gene products influence a trait  • Typically, one gene product suppresses the effect  ...
Epistasis in Coat Colors
EB        Eb        eB         eb     EEBB     EEBb       EeBB       EeBbEB   black    black      black      black     EEB...
Epistasis in Chicken Combs
Pleiotropy Pleiotropy  • One gene product    influences two or    more traits  • Example: Some tall,    thin athletes hav...
11.5 Linkage Groups The farther apart two genes are on a  chromosome, the more often crossing over  occurs between them ...
Linkage and Crossing Over
Parental       AC                                          acgeneration                                     XF1 offspring ...
Animation: Crossover review
The Distance Between Genes The probability that a crossover event will  separate alleles of two genes is proportional to ...
11.6 Genes and the Environment Expression of some genes is affected by  environmental factors such as temperature,  altit...
Effects of Temperatureon Gene Expression Enzyme tyrosinase, works at low temperatures
Animation: Coat color in the Himalayanrabbit
Effects of Altitudeon Gene Expression
Height (centimeters) Height (centimeters) Height (centimeters)                                                            ...
Effects of Predationon Gene Expression Predators of daphnias emit chemicals that  trigger a different phenotype
Fig. 11-18a, p. 179
Fig. 11-18b, p. 179
11.7 ComplexVariations in Traits Individuals of most  species vary in some  of their shared traits Many traits (such as ...
Continuous Variation Continuous variation  • Traits with a range of small differences  • The more factors that influence ...
Continuous Variation and the Bell Curve
Fig. 11-19a, p. 180
Fig. 11-19b, p. 180
Fig. 11-19c, p. 180
Animation: Continuous variation inheight
Regarding the Unexpected Phenotype Phenotype results from complex interactions  among gene products and the environment  ...
11.4-11.7 Key ConceptsVariations on Mendel’s Theme Not all traits appear in Mendelian inheritance  patterns  • An allele ...
Animation: Testcross
Animation: Coat color in Labradorretrievers
Animation: Comb shape in chickens
Animation: F2 ratios interaction
Animation: Genetic terms
Animation: Incomplete dominance
Animation: Monohybrid cross
Animation: Pleiotropic effects of Marfansyndrome
Video: Genetics of skin color
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Chapter11- Mendels

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Chapter11- Mendels

  1. 1. Observing Patterns in Inherited Traits Chapter 11
  2. 2. Impacts, Issues:The Color of Skin Like most human traits, skin color has a genetic basis; more than 100 gene products affect the synthesis and deposition of melanins
  3. 3. 11.1 Mendel, Pea Plants,and Inheritance Patterns Recurring inheritance patterns are observable outcomes of sexual reproduction Before the discovery of genes, it was thought that inherited traits resulted from a blend of parental characters
  4. 4. Mendel’s Experimental Approach Mendel was a monk with training in plant breeding and mathematics He studied the garden pea (Pisum sativum), which breeds true for a number of traits
  5. 5. Garden Pea Plant:Self Fertilization and Cross-Fertilization
  6. 6. carpel antherA Garden pea flower, cut in half. Sperm form inpollen grains, which originate in male floral parts(anthers). Eggs develop, fertilization takes place,and seeds mature in female floral parts (carpels).B Pollen from a plant that breeds true for purple flowers isbrushed onto a floral bud of a plant that breeds true for whiteflowers. The white flower had its anthers snipped off. Artificialpollination is one way to ensure that a plant will not self-fertilize.C Later, seeds develop inside pods of the cross-fertilizedplant. An embryo in each seed develops into a mature pea plant.D Each new plant’s flower color is indirect butobservable evidence that hereditary materialhas been transmitted from the parent plants. Fig. 11-3, p. 170
  7. 7. Animation: Crossing garden pea plants
  8. 8. Terms Used in Modern Genetics Genes • Heritable units of information about traits • Parents transmit genes to offspring • Each gene has a specific locus on a chromosome Diploid cells (chromosome number 2n) have pairs of genes on homologous chromosomes
  9. 9. Terms Used in Modern Genetics A mutation is a permanent change in a gene • May cause a trait to change • Alleles are different molecular forms of a gene A hybrid has nonidentical alleles for a trait • Offspring of a cross between two individuals that breed true for different forms of a trait are hybrids
  10. 10. Terms Used in Modern Genetics An individual with nonidentical alleles of a gene is heterozygous for that gene An individual with identical alleles of a gene is homozygous for that gene
  11. 11. Terms Used in Modern Genetics An allele is dominant if its effect masks the effect of a recessive allele paired with it • Capital letters (A) signify dominant alleles; lowercase letters (a) signify recessive alleles • Homozygous dominant (AA) • Homozygous recessive (aa) • Heterozygous (Aa)
  12. 12. Terms Used in Modern Genetics Gene expression • The process by which information in a gene is converted to a structural or functional part of a cell or body • Expressed genes determine traits
  13. 13. Terms Used in Modern Genetics Genotype • The particular alleles an individual carries Phenotype • An individual’s observable traits
  14. 14. Terms Used in Modern Genetics P stands for parents, F for filial (offspring) F1: First generation offspring of parents F2: Second generation offspring of parents
  15. 15. 11.1 Key ConceptsWhere Modern Genetics Started Gregor Mendel gathered the first experimental evidence of the genetic basis of inheritance His meticulous work gave him clues that heritable traits are specified in units The units, which are distributed into gametes in predictable patterns, were later identified as genes
  16. 16. 11.2 Mendel’s Law of Segregation Garden pea plants inherit two “units” of information for a trait, one from each parent
  17. 17. Testcrosses Testcross • A method of determining if an individual is heterozygous or homozygous dominant • An individual with unknown genotype is crossed with one that is homozygous recessive (AA x aa) or (Aa x aa)
  18. 18. Monohybrid Experiments Monohybrid experiments • Testcrosses that check for a dominance relationship between two alleles at a single locus • May be crosses between true breeding (homozygous) individuals (AA x aa), or between identical heterozygotes (Aa x Aa)
  19. 19. Mendel’s Monohybrid Experiments Mendel used monohybrid experiments to find dominance relationships among pea plant traits • When he crossed plants that bred true for white flowers with plants that bred true for purple flowers, all F1 plants had purple flowers • When he crossed two F1 plants, ¾ of the F2 plants had purple flowers, ¼ had white flowers
  20. 20. Segregation of Alleles at a Gene Locus
  21. 21. homozygous homozygousdominant parent recessive parent (chromosomes duplicated before meiosis) meiosis I meiosis II (gametes) (gametes) fertilization produces heterozygous offspring Fig. 11-5, p. 172
  22. 22. homozygous homozygousdominant parent recessive parent (chromosomes duplicated before meiosis) meiosis I meiosis II (gametes) (gametes) fertilization produces heterozygous Stepped Art offspring Fig. 11-5, p. 172
  23. 23. Mendel’s Monohybrid Experiments
  24. 24. Trait Dominant Recessive F2 Dominant-to-Studied Form Form Recessive RatioSeedshape 5,474 round 1,850 wrinkled 2.98 to 1Seedcolor 6,022 yellow 2,001 green 3.01 to 1Podshape 882 inflated 299 wrinkled 2.95 to 1Podcolor 428 green 152 yellow 2.82 to 1Flowercolor 705 purple 224 white 3.15 to 1Flowerposition 651 along stem 207 at tip 3.14 to 1Stemlength 787 tall 277 dwarf 2.84 to 1 Fig. 11-6, p. 172
  25. 25. Calculating Probabilities Probability • A measure of the chance that a particular outcome will occur Punnett square • A grid used to calculate the probability of genotypes and phenotypes in offspring
  26. 26. Construction of a Punnett Square
  27. 27. Phenotype Ratiosin a Monohybrid Experiment
  28. 28. Phenotype Ratiosin a Monohybrid Experiment
  29. 29. Fig. 11-7, p. 173
  30. 30. female gametes A a A a A a A amale gametes A A A Aa A AA Aa a aa a Aa aa a Aa aa a Aa aa A From left to right, step-by-step construction of a Punnett square. Circles signify gametes, and letters signify alleles: A is dominant; a is recessive. The genotypes of the resulting offspring are inside the squares. Fig. 11-7a, p. 173
  31. 31. F1 offspring aaTrue-breeding homozygousrecessive parent plant a a Aa Aa A Aa Aa AA A Aa AaTrue-breeding homozygous Aa Aadominant parent plant B A cross between two plants that breed true for different forms of a trait produces F1 offspring that are identically heterozygous. Fig. 11-7b, p. 173
  32. 32. F2 offspring AaHeterozygousF1 offspring A a AA Aa A AA Aa Aa a Aa aaHeterozygousF1 offspring Aa aaC A cross between the F1 offspring is the monohybrid experiment. Thephenotype ratio of F2 offspring in this example is 3:1 (3 purple to 1 white). Fig. 11-7c, p. 173
  33. 33. Mendel’s Law of Segregation Mendel observed a phenotype ratio of 3:1 in the F2 offspring of his monohybrid crosses • Consistent with the probability of the aa genotype in the offspring of a heterozygous cross (Aa x Aa) This is the basis of Mendel’s law of segregation • Diploid cells have pairs of genes on pairs of homologous chromosomes • The two genes of each pair separate during meiosis, and end up in different gametes
  34. 34. 11.2 Key ConceptsInsights from Monohybrid Experiments Some experiments yielded evidence of gene segregation: When one chromosome separates from its homologous partner during meiosis, the alleles on those chromosomes also separate and end up in different gametes
  35. 35. 11.3 Mendel’s Lawof Independent Assortment Mendel’s law of independent assortment • Many genes are sorted into gametes independently of other genes
  36. 36. Dihybrid Experiments Dihybrid experiments • Tests for dominance relationships between alleles at two loci • Individuals that breed true for two different traits are crossed (AABB x aabb) • F2 phenotype ratio is 9:3:3:1 (four phenotypes) • Individually, each dominant trait has an F2 ratio of 3:1 – inheritance of one trait does not affect inheritance of the other
  37. 37. Independent Assortment at Meiosis
  38. 38. One of two possible alignments The only other possible alignmenta Chromosome A Aa a A Aa aalignments atmetaphase I: B Bb b b bB Bb The resulting A A a a A A a aalignments atmetaphase II: B B b b b b B Bc Possible B A A B b a a b b A A b B a a Bcombinationsof alleles ingametes: AB ab Ab aB Fig. 11-8, p. 174
  39. 39. One of two possible alignments The only other possible alignmenta Chromosome A Aa a A Aa aalignments atmetaphase I: B Bb b b bB Bb The resulting A A a a A A a aalignments atmetaphase II: B B b b b b B Bc Possible B A A B b a a b b A A b B a a Bcombinationsof alleles ingametes: AB ab Ab aB Stepped Art Fig. 11-8, p. 174
  40. 40. Mendel’s Dihybrid Experiments
  41. 41. Fig. 11-9a, p. 175
  42. 42. parent plant parent plant homozygous homozygousP for purple for whitegeneration flowers flowers A Meiosis in homozygous and long and short individuals results in one stems stems kind of gamete. aabb AABB B A cross between plants homozygous for two different traits AB x ab yields one possible combination of gametes: Fig. 11-9a, p. 175
  43. 43. Fig. 11-9b, p. 175
  44. 44. AaBb AaBb AaBbF1 All F1 offspring are AaBb,generation with purple flowers and tall stems. C Meiosis in AaBb dihybrid plants results in four kinds of gametes: AB Ab aB abF2 These gametes can meet up in one of 16generation possible wayswhen the dihybrids are crossed (AaBb X AaBb): Fig. 11-9b, p. 175
  45. 45. Fig. 11-9c, p. 175
  46. 46. AB Ab aB ab AB AABB AABb AaBB AaBb Ab AABb AAbb AaBb Aabb aB AaBB AaBb aaBB aaBb ab AaBb Aabb aaBb aabbD Out of 16 possible genetic outcomes of this dihybrid cross, 9 will result in plants thatare purple-flowered and tall; 3, purple-flowered and short; 3, white-flowered and tall;and 1, white-flowered and short. The ratio of phenotypes of this dihybrid cross is 9:3:3:1. Fig. 11-9c, p. 175
  47. 47. Animation: Dihybrid cross
  48. 48. Mendel’s Law of IndependentAssortment Mendel’s dihybrid experiments showed that “units” specifying one trait segregated into gametes separately from “units” for other traits Exception: Genes that have loci very close to one another on a chromosome tend to stay together during meiosis
  49. 49. 11.3 Key ConceptsInsights from Dihybrid Experiments Some experiments yielded evidence of independent assortment: Genes are typically distributed into gametes independently of other genes
  50. 50. 11.4 Beyond Simple Dominance Mendel focused on traits based on clearly dominant and recessive alleles; however, the expression patterns of genes for some traits are not as straightforward
  51. 51. Codominance in ABO Blood Types Codominance • Two nonidentical alleles of a gene are both fully expressed in heterozygotes, so neither is dominant or recessive • May occur in multiple allele systems Multiple allele systems • Genes with three or more alleles in a population • Example: ABO blood types
  52. 52. Codominance in ABO Blood Types
  53. 53. AA BB or orGenotypes: AO AB BO OOPhenotypes(Blood type): A AB B O Fig. 11-10, p. 176
  54. 54. Animation: Codominance: ABO bloodtypes
  55. 55. Incomplete Dominance Incomplete dominance • One allele is not fully dominant over its partner • The heterozygote’s phenotype is somewhere between the two homozygotes, resulting in a 1:2:1 phenotype ratio in F2 offspring Example: Snapdragon color • RR is red • Rr is pink • rr is white
  56. 56. Incomplete Dominance in Snapdragons
  57. 57. Fig. 11-11a, p. 176
  58. 58. homozygous homozygous heterozygous F1 x parent (rr)parent (RR) offspring (Rr)A Cross a red-flowered with a white-flowered plant,and all of the F1 offspring will be pink. Fig. 11-11a, p. 176
  59. 59. Fig. 11-11b, p. 176
  60. 60. R rB Cross two F1 plants, Rand the three phenotypes RR Rrof the F2 offspring willoccur in a 1:2 :1 ratio: r Rr rr Fig. 11-11b, p. 176
  61. 61. Epistasis Epistasis • Two or more gene products influence a trait • Typically, one gene product suppresses the effect of another Example: Coat color in dogs • Alleles B and b designate colors (black or brown) • Two recessive alleles ee suppress color
  62. 62. Epistasis in Coat Colors
  63. 63. EB Eb eB eb EEBB EEBb EeBB EeBbEB black black black black EEBb EEbb EeBb EebbEb black chocolate black chocolate EeBB EeBb eeBB eeBbeB black yellow yellow black EeBb Eebb eeBb eebbeb black chocolate yellow yellow Fig. 11-13a, p. 177
  64. 64. Epistasis in Chicken Combs
  65. 65. Pleiotropy Pleiotropy • One gene product influences two or more traits • Example: Some tall, thin athletes have Marfan syndrome, a potentially fatal genetic disorder
  66. 66. 11.5 Linkage Groups The farther apart two genes are on a chromosome, the more often crossing over occurs between them Linkage group • All genes on one chromosome • Linked genes are very close together; crossing over rarely occurs between them
  67. 67. Linkage and Crossing Over
  68. 68. Parental AC acgeneration XF1 offspring All AaCc meiosis, gamete formationGametes Most gametes have A smaller number have parental genotypes recombinant genotypes Fig. 11-15, p. 178
  69. 69. Animation: Crossover review
  70. 70. The Distance Between Genes The probability that a crossover event will separate alleles of two genes is proportional to the distance between those genes
  71. 71. 11.6 Genes and the Environment Expression of some genes is affected by environmental factors such as temperature, altitude, or chemical exposure The result may be variation in traits
  72. 72. Effects of Temperatureon Gene Expression Enzyme tyrosinase, works at low temperatures
  73. 73. Animation: Coat color in the Himalayanrabbit
  74. 74. Effects of Altitudeon Gene Expression
  75. 75. Height (centimeters) Height (centimeters) Height (centimeters) 60 a Mature cutting at high elevation (3,060 meters above sea level) 0 60 b Mature cutting at mid- elevation (1,400 meters above sea level) 0 60 c Mature cutting at low elevation (30 meters above sea level) 0 Fig. 11-17, p. 179
  76. 76. Effects of Predationon Gene Expression Predators of daphnias emit chemicals that trigger a different phenotype
  77. 77. Fig. 11-18a, p. 179
  78. 78. Fig. 11-18b, p. 179
  79. 79. 11.7 ComplexVariations in Traits Individuals of most species vary in some of their shared traits Many traits (such as eye color) show a continuous range of variation
  80. 80. Continuous Variation Continuous variation • Traits with a range of small differences • The more factors that influence a trait, the more continuous the distribution of phenotype Bell curve • When continuous phenotypes are divided into measurable categories and plotted as a bar chart, they form a bell-shaped curve
  81. 81. Continuous Variation and the Bell Curve
  82. 82. Fig. 11-19a, p. 180
  83. 83. Fig. 11-19b, p. 180
  84. 84. Fig. 11-19c, p. 180
  85. 85. Animation: Continuous variation inheight
  86. 86. Regarding the Unexpected Phenotype Phenotype results from complex interactions among gene products and the environment • Enzymes and other gene products control steps of most metabolic pathways • Mutations, interactions among genes, and environmental conditions may affect one or more steps
  87. 87. 11.4-11.7 Key ConceptsVariations on Mendel’s Theme Not all traits appear in Mendelian inheritance patterns • An allele may be partly dominant over a nonidentical partner, or codominant with it • Multiple genes may influence a trait; some genes influence many traits • The environments also influences gene expression
  88. 88. Animation: Testcross
  89. 89. Animation: Coat color in Labradorretrievers
  90. 90. Animation: Comb shape in chickens
  91. 91. Animation: F2 ratios interaction
  92. 92. Animation: Genetic terms
  93. 93. Animation: Incomplete dominance
  94. 94. Animation: Monohybrid cross
  95. 95. Animation: Pleiotropic effects of Marfansyndrome
  96. 96. Video: Genetics of skin color

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