1. Biology Sylvia S. Mader Michael Windelspecht Chapter 11 Mendelian Patterns of Inheritance Lecture Outline Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. See separate FlexArt PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes. 1

2. 2 Outline 11.1 Gregor Mendel 11.2 Mendel’s Laws 11.3 Extending the Range of Mendelian Genetics

3. 11.1 Gregor Mendel Concept of Blending Inheritance:  Parents of contrasting appearance produce offspring of intermediate appearance  Popular concept during Mendel’s time Mendel’s findings were in contrast with this  He formulated the Particulate Theory of Inheritance Inheritance involves reshuffling of genes from generation to generation 3

4. Gregor Mendel Austrian monk  Studied science and mathematics at the University of Vienna  Conducted breeding experiments with the garden pea Pisum sativum  Carefully gathered and documented mathematical data from his experiments Formulated fundamental laws of heredity in the early 1860s  Had no knowledge of cells or chromosomes  Did not have a microscope 4

5. Gregor Mendel 5 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. © Ned M. Seidler/Nationa1 Geographic Image Collection

6. 6 Gregor Mendel The garden pea:  Organism used in Mendel’s experiments  A good choice for several reasons: Easy to cultivate Short generation Normally self-pollinating, but can be cross- pollinated by hand True-breeding varieties were available Simple, objective traits

7. Garden Pea Anatomy 7 stamen anther a. Flower Structure filament stigma style ovules in ovary carpel Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

8. 8 All peas are yellow when one parent produces yellow seeds and the other parent produces green seeds. Brushing on pollen from another plant Cutting away anthers Garden Pea Anatomy Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

9. Garden Pea Anatomy Trait *Dominant Characteristics *Recessive Stem length Pod shape Seed shape Seed color Flower position Flower color Pod color b. Green Purple Axial Yellow Round Inflated TallShort Constricted Wrinkled Green Terminal White Yellow Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

10. 11.2 Mendel’s Laws Mendel performed cross-breeding experiments  Used “true-breeding” (homozygous) plants  Chose varieties that differed in only one trait (monohybrid cross)  Performed reciprocal crosses Parental generation = P First filial generation offspring = F 1 Second filial generation offspring = F 2  Formulated the Law of Segregation 10

11. Monohybrid Cross done by Mendel 11 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. TTtt Phenotypic Ratio short1 tall3 Allele Key T tall plant = t short plant =

12. Monohybrid Cross done by Mendel 12 P generation TTtt Phenotypic Ratio short1 tall3 Allele Key T tall plant = t short plant = Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

13. Monohybrid Cross done by Mendel 13 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. P generation TTtt t T P gametes Phenotypic Ratio short 1 tall 3 Allele Key T tall plant = t short plant =

14. Monohybrid Cross done by Mendel 14 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. tt P generation TTtt t T Tt P gametes F 1 generation Phenotypic Ratio short1 tall3 Allele Key T tall plant = t short plant =

15. Monohybrid Cross done by Mendel 15 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. eggs sperm P generation Tt T t TTtt t T Tt P gametes F1 gametes F1 generation Phenotypic Ratio short 1 tall 3 Allele Key T tall plant = t short plant =

16. Monohybrid Cross done by Mendel Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. eggs sperm P generation Tt T t TT tt t T Tt TT P gametes F 1 gametes F 1 generation Phenotypic Ratio short 1 tall 3 Allele Key T tall plant = t short plant = 16

17. Monohybrid Cross done by Mendel 17 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. eggs sperm Tt T t TTtt t T Tt TTTt F 1 gametes Phenotypic Ratio short1 tall 3 Allele key F 1 generation P gametes F 1 generation T tall plant = t short plant =

18. Monohybrid Cross done by Mendel 18 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. eggs sperm P generation Tt T t TTtt t T Tt TTTt P gametes F 1 gametes F 1 generation Phenotypic Ratio short 1 tall 3 Allele Key T tall plant = t short plant =

19. Monohybrid Cross done by Mendel 19 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. eggs sperm Offspring P generation Tt T t TTtt t T Tt TTTt tt P gametes F 1 gametes F 2 generation F 1 generation Phenotypic Ratio short1 tall3 Allele Key T tall plant = t short plant =

20. Mendel’s Laws Law of Segregation:  Each individual has a pair of factors (alleles) for each trait  The factors (alleles) segregate (separate) during gamete (sperm & egg) formation  Each gamete contains only one factor (allele) from each pair of factors  Fertilization gives the offspring two factors for each trait 20

21. Mendel’s Laws Classical Genetics and Mendel’s Cross:  Each trait in a pea plant is controlled by two alleles (alternate forms of a gene)  Dominant allele (capital letter) masks the expression of the recessive allele (lower-case)  Alleles occur on a homologous pair of chromosomes at a particular gene locus Homozygous = identical alleles Heterozygous = different alleles 21

22. Classical View of Homologous Chromosomes 22 Replication alleles at a gene locus sister chromatids b. Sister chromatids of duplicated chromosomes have same alleles for each gene. a. Homologous chromosomes have alleles for same genes at specific loci. G R S t G R S t G R S t g r s T g r s T g r s T Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

23. Relationship Between Observed Phenotype and F 2 Offspring Trait Stem length Pod shape Seed shape Seed color Flower position Flower color Pod color Dominant Characteristics Recessive Tall Inflated Round Yellow Axial Purple Green Short Constricted Wrinkled Green Terminal White Yellow Dominant F 2 Results RatioRecessive Totals: 2.84:1277787 8822992.95:1 2.96:1 3.01:1 3.14:1 3.15:1 2.82:1 2.98:1 2,001 1,8505,474 6,022 651 705 428 14,949 207 224 152 5,010 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

24. Mendel’s Laws Genotype  Refers to the two alleles an individual has for a specific trait  If identical, genotype is homozygous  If different, genotype is heterozygous Phenotype  Refers to the physical appearance of the individual 24

25. Mendel’s Laws A dihybrid cross uses true-breeding plants differing in two traits Mendel tracked each trait through two generations.  Started with true-breeding plants differing in two traits  The F 1 plants showed both dominant characteristics  F 1 plants self-pollinated  Observed phenotypes among F 2 plants Mendel formulated the Law of Independent Assortment  The pair of factors for one trait segregate independently of the factors for other traits  All possible combinations of factors can occur in the gametes P generation is the parental generation in a breeding experiment. F 1 generation is the first-generation offspring in a breeding experiment. F 2 generation is the second-generation offspring in a breeding experiment 25

26. Dihybrid Cross Done by Mendel Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. × = = = = T t G g 9 3 3 1 ttggTTGG P generation P gametes F 1 generation F 1 gametes F 2 generation sperm eggs TtGg TG tg tGTgTG TtGg Tg tG tg TTGGTTGgTtGG TtggTtGgTTggTTGg ttGgttGGTtGgTtGG ttggttGgTtggTtGg Allele Key Offspring Phenotypic Ratio Yellow pod green pod short plant tall plant tall plant, green pod tall plant, yellow pod short plant, green pod short plant, yellow pod

27. Independent Assortment and Segregation during Meiosis 27 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. A a B b Parent cell has two pairs of homologous chromosomes.

28. Independent Assortment and Segregation during Meiosis 28 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. A AA a aa B BB b bb either Parent cell has two pairs of homologous chromosomes.

29. Independent Assortment and Segregation during Meiosis 29 A AA a aa B BB b bb AA bbBB aa either or Parent cell has two pairs of homologous chromosomes. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

30. Independent Assortment and Segregation during Meiosis 30 A AA a aa B BB b bb A A bbBB aa either or Parent cell has two pairs of homologous chromosomes. All orientations of ho- mologous chromosomes are possible at meta- phase I in keeping with the law of independent assortment. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

31. Independent Assortment and Segregation during Meiosis 31 A AA AA a a a a a B BB BB b bb AA bbBB aa bb either or Parent cell has two pairs of homologous chromosomes. All orientations of ho- mologous chromosomes are possible at metaphase I in keeping with the law of independent assortment. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

32. Independent Assortment and Segregation during Meiosis 32 A AA AA a a a a a AA aa B BB BB BB b bb AA bbBB aa bb bb either or Parent cell has two pairs of homologous chromosomes. All orientations of ho- mologous chromosomes are possible at metaphase I in keeping with the law of independent assortment. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

33. Independent Assortment and Segregation during Meiosis 33 A AA AA a a a a a AA aa B BB BB BB b bb AA bbBB aa bb bb either or Parent cell has two pairs of homologous chromosomes. All orientations of ho- mologous chromosomes are possible at meta- phase I in keeping with the law of independent assortment. At metaphase II, each daughter cell has only one member of each homologous pair in keeping with the law of segregation Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

34. Independent Assortment and Segregation during Meiosis 34 Parent cell has two pairs of homologous chromosomes. All possible combi - tions of chromosomes and alleles occur in the gametes as suggested by Mendel's two laws. All orientations of ho- mologous chromosomes are possible at metaphase I in keeping with the law of Independent assortment. At metaphase II, each daughter cell has only one member of each homologous pair in keeping with the law of segregation A AA AA A A AB ab Ab aB a a a a a a a A A b A aa a B B BB B B B B B B a B b bb AA bbBB aa b b b b b A b b either or Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

35. 35 Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. Animation

36. Mendel’s Laws Punnett Square  Table listing all possible genotypes resulting from a cross All possible sperm genotypes are lined up on one side All possible egg genotypes are lined up on the other side Every possible zygote genotypes are placed within the squares 36

37. Mendel’s Laws Punnett Square  Allows us to easily calculate probability, of genotypes and phenotypes among the offspring  Punnett square in next slide shows a 50% (or ½) chance The chance of E = ½ The chance of e = ½  An offspring will inherit: The chance of EE =½  ½=¼ The chance of Ee =½  ½=¼ The chance of eE =½  ½=¼ The chance of ee =½  ½=¼ 37

38. Punnett Square 38 eggs spem Punnett square Offspring Parents Ee E e Ee EE Ee Allele key Phenotypic Ratio unattached earlobes 3 1 E = e = unattached earlobes attached earlobes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ee

39. Mendel’s Laws Testcrosses  Individuals with recessive phenotype always have the homozygous recessive genotype  However, individuals with dominant phenotype have indeterminate genotype May be homozygous dominant, or Heterozygous  A testcross determines the genotype of an individual having the dominant phenotype 39

40. One-Trait Testcross 40

41. One-Trait Testcross 41 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. b. tT Tt Offspring eggs sperm TTtt Allele Key Phenotypic Ratio All tall plants T = tall plant t = short plant

42. 42 Mendel’s Laws Two-trait testcross:  An individual with both dominant phenotypes is crossed with an individual with both recessive phenotypes.  If the individual with the dominant phenotypes is heterozygous for both traits, the expected phenotypic ration is 1:1:1:1.

43. Mendel’s Laws Genetic disorders are medical conditions caused by alleles inherited from parents Autosome - Any chromosome other than a sex chromosome (X or Y) Genetic disorders caused by genes on autosomes are called autosomal disorders  Some genetic disorders are autosomal dominant An individual with AA has the disorder An individual with Aa has the disorder An individual with aa does NOT have the disorder  Other genetic disorders are autosomal recessive An individual with AA does NOT have the disorder An individual with Aa does NOT have the disorder, but is a carrier An individual with aa DOES have the disorder 43

44. Autosomal Recessive Pedigree 44 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. I II III IV Key Generations Autosomal recessive disorders Most affected children have unaffected parents. Heterozygotes (Aa) have an unaffected phenotype. Two affected parents will always have affected children. Close relatives who reproduce are more likely to have affected children. Both males and females are affected with equal frequency. A? aa A? Aa A? Aa * A? aa aa = affected Aa = carrier (unaffected) AA = unaffected A? = unaffected (one allele unknown)

45. Autosomal Dominant Pedigree 45 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Affected children will usually have an affected parent. Heterozygotes (Aa) are affected. Two affected parents can produce an unaffected child. Two unaffected parents will not have affected children. Both males and females are affected with equal frequency. AA = affected Aa = affected A? = affected (one allele unknown) aa = unaffected I II III Aa aa Aa * A? aa Aa Key Generations Autosomal dominant disorders

46. Mendel’s Laws Autosomal Recessive Disorders:  Methemoglobinemia Relatively harmless disorder Accumulation of methemoglobin in the blood causes skin to appear bluish-purple  Cystic Fibrosis Mucus in bronchial tubes and pancreatic ducts is particularly thick and viscous 46

47. Methemoglobinemia 47 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Courtesy Division of Medical Toxicology, University of Virginia

48. Cystic Fibrosis 48 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cl - H2OH2O H2OH2O H2OH2O thick mucus defective channel nebulizer percussion vest © Pat Pendarvis

49. Mendel’s Laws Autosomal Dominant Disorders  Osteogenesis Imperfecta Weakened, brittle bones Most cases are caused by mutation in genes required for the synthesis of type I collagen  Hereditary Spherocytosis Caused by a mutation in the ankyrin-1 gene Red blood cells become spherical, are fragile, and burst easily 49

50. 11.3 Extending the Range of Mendelian Genetics Some traits are controlled by multiple alleles (multiple allelic traits) The gene exists in several allelic forms (but each individual only has two alleles) ABO blood types  The alleles: I A = A antigen on red blood cells, anti-B antibody in plasma I B = B antigen on red blood cells, anti-A antibody in plasma i = Neither A nor B antigens on red blood cells, both anti-A and anti- B antibodies in plasma The ABO blood type is also an example of codominance  More than one allele is fully expressed  Both I A and I B are expressed in the presence of the other 50

51. ABO Blood Type 51 Genotype I A I A, I A i I B I B, I B i I A I B ii Phenotype A B AB O

52. Extending the Range of Mendelian Genetics Incomplete Dominance:  Heterozygote has a phenotype intermediate between that of either homozygote Homozygous red has red phenotype Homozygous white has white phenotype Heterozygote has pink (intermediate) phenotype  Phenotype reveals genotype without a test cross 52

53. Incomplete Dominance 53 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. R 1 R 2 R 1 R 2 R 1 R 2 R 1 R 2 R 1 R 1 R 2 R 2 R 1 R 2 R 1 R 2 eggs sperm Offspring Key 1 R 1 R 1 2 R 1 R 2 1 R 2 R 2 red pink white

54. 54 Extending the Range of Mendelian Genetics Human examples of incomplete dominance:  Familial Hypercholesterolemia (FH) Homozygotes for the mutant allele develop fatty deposits in the skin and tendons and may have heart attacks during childhood Heterozygotes may suffer heart attacks during early adulthood Homozygotes for the normal allele do not have the disorder

55. 55 Extending the Range of Mendelian Genetics Human examples of incomplete dominance:  Incomplete penetrance The dominant allele may not always lead to the dominant phenotype in a heterozygote Many dominant alleles exhibit varying degrees of penetrance Example: polydactyly –Extra digits on hands, feet, or both –Not all individuals who inherit the dominant polydactyly allele will exhibit the trait

56. Extending the Range of Mendelian Genetics Pleiotropy occurs when a single mutant gene affects two or more distinct and seemingly unrelated traits. Marfan syndrome is pleiotropic and results in the following phenotypes:  disproportionately long arms, legs, hands, and feet  a weakened aorta  poor eyesight 56

57. Marfan Syndrome 57 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chest wall deformities Long, thin fingers, arms, legs Scoliosis (curvature of the spine) Flat feet Long, narrow face Loose joints SkeletonSkinLungsEyes Lens dislocation Severe nearsightedness Collapsed lungs Stretch marks in skin Recurrent hernias Dural ectasia: stretching of the membrane that holds spinal fluid Mitral valve prolapse Enlargement of aorta Heart and blood vessels Aneurysm Aortic wall tear Connective tissue defects (Left): © AP/Wide World Photos; (Right): © Ed Reschke; (Sickled cells, p. 203): © Phototake, Inc./Alamy

58. Extending the Range of Mendelian Genetics Polygenic Inheritance:  Occurs when a trait is governed by two or more genes having different alleles  Each dominant allele has a quantitative effect on the phenotype  These effects are additive  Results in continuous variation of phenotypes within a population  The traits may also be affected by the environment  Examples Human skin color Height Eye color 58

59. Polygenic Inheritance 59 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. aabbcc Aabbcc AaBbcc AaBbCc AABbCc AABBCc AABBCC 20 — 64 15 — 64 6 — 1 Proportion of Population Genotype Examples F 2 generation — F 1 generation P generation

60. Extending the Range of Mendelian Genetics X-Linked Inheritance  In mammals The X and Y chromosomes determine gender Females are XX Males are XY 60

61. Extending the Range of Mendelian Genetics X-Linked Inheritance  The term X-linked is used for genes that have nothing to do with gender X-linked genes are carried on the X chromosome. The Y chromosome does not carry these genes Discovered in the early 1900s by a group at Columbia University, headed by Thomas Hunt Morgan. –Performed experiments with fruit flies »They can be easily and inexpensively raised in simple laboratory glassware »Fruit flies have the same sex chromosome pattern as humans 61

62. X – Linked Inheritance 62 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. XrYXrY XRYXRY XRXR XrXr Y XrYXrY XrXr XRXR Y Offspring eggs sperm P generation P gametes F 2 generation F 1 generation F 1 gametes Allele Key = = XRXR XrXr red eyes white eyes Phenotypic Ratio all red-eyed red-eyed white-eyed females: males: 1 1 XRYXRY XRXrXRXr XRXRXRXR XRXR XRXrXRXr XRXRXRXR

63. X – Linked Inheritance

64. Extending the Range of Mendelian Genetics Several X-linked recessive disorders occur in humans:  Color blindness The allele for the blue-sensitive protein is autosomal The alleles for the red- and green-sensitive pigments are on the X chromosome.  Menkes syndrome Caused by a defective allele on the X chromosome Disrupts movement of the metal copper in and out of cells. Phenotypes include kinky hair, poor muscle tone, seizures, and low body temperature  Muscular dystrophy Wasting away of the muscle Caused by the absence of the muscle protein dystrophin  Adrenoleukodystrophy X-linked recessive disorder Failure of a carrier protein to move either an enzyme or very long chain fatty acid into peroxisomes.  Hemophilia Absence or minimal presence of clotting factor VIII or clotting factor IX Affected person’s blood either does not clot or clots very slowly. 64

65. X-Linked Recessive Pedigree 65 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. XBXBXBXB XbYXbY grandfather daughterXBXbXBXb XBYXBYXBYXBYXbXbXbXb XbYXbY XBXbXBXb grandson XBYXBYXBXBXBXB XbYXbY Key X B X B = Unaffected female X B X b = Carrier female X b X b = Color-blind female X b Y = Unaffected male X b Y = Color-blind male X-Linked Recessive Disorders More males than females are affected. An affected son can have parents who have the normal phenotype. For a female to have the characteristic, her father must also have it. Her mother must have it or be a carrier. The characteristic often skips a generation from the grandfather to the grandson. If a woman has the characteristic, all of her sons will have it.

66. Muscular Dystrophy 66 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (Abnormal): Courtesy Dr. Rabi Tawil, Director, Neuromuscular Pathology Laboratory, University of Rochester Medical Center; (Boy): Courtesy Muscular Dystrophy Association; (Normal): Courtesy Dr. Rabi Tawil, Director, Neuromuscular Pathology Laboratory, University of Rochester Medical Center. abnormal muscle normal tissue fibrous tissue