2. 1 Mendelelian Genetics copyright cmassengale

3. A Tale of Two Families copyright cmassengale2 Modes of inheritance are the rules explaining the common patterns of inheritance. Huntington’s Disease and Cystic Fibrosis demonstrate two important modes of inheritance. HD is autosomal dominant and CF is autosomal recessive.

4. Fig. 4.1 Autosomal Dominant – affects both sexes and appears every generation

5. Fig. 4.2 Autosomal Recessive – affects both sexes and skip generations through carriers

6. 5 Gregor Mendel (1822-1884) Responsible for the Laws governing Inheritance of Traits copyright cmassengale

7. 6 Gregor Johann Mendel  Austrian monk  Studied the inheritance of traits in pea plants  Developed the laws of inheritance  Mendel's work was not recognized until the turn of the 20th century copyright cmassengale

8. 7 Gregor Johann Mendel  Between 1856 and 1863, Mendel cultivated and tested some 28,000 pea plants  He found that the plants' offspring retained traits of the parents  Called the “Father of Genetics" copyright cmassengale

9. 8 Site of Gregor Mendel’s experimental garden in the Czech Republic copyright cmassengale

10. 9  Mendel stated that physical traits are inherited as “particles”  Mendel did not know that the “particles” were actually Chromosomes & DNA Particulate Inheritance copyright cmassengale

11. 10 Genetic Terminology  Trait - any characteristic that can be passed from parent to offspring  Heredity - passing of traits from parent to offspring  Genetics - study of heredity copyright cmassengale

12. 11 Types of Genetic Crosses  Monohybrid cross - cross involving a single trait e.g. flower color  Dihybrid cross - cross involving two traits e.g. flower color & plant height copyright cmassengale

13. 12 Punnett Square Used to help solve genetics problems copyright cmassengale

14. 13copyright cmassengale

15. 14 Designer “Genes”  Alleles - two forms of a gene (dominant & recessive)  Dominant - stronger of two genes expressed in the hybrid; represented by a capital letter (R)  Recessive - gene that shows up less often in a cross; represented by a lowercase letter (r) copyright cmassengale

16. 15 More Terminology  Genotype - gene combination for a trait (e.g. RR, Rr, rr)  Phenotype - the physical feature resulting from a genotype (e.g. red, white) copyright cmassengale

17. 16 Genotype & Phenotype in Flowers Genotype of alleles: R = red flower r = yellow flower All genes occur in pairs, so 2 alleles affect a characteristic Possible combinations are: GenotypesRR Rrrr PhenotypesRED RED YELLOW copyright cmassengale

18. 17 Genotypes  Homozygous genotype - gene combination involving 2 dominant or 2 recessive genes (e.g. RR or rr); also called pure  Homozygous genotype - gene combination involving 2 dominant or 2 recessive genes (e.g. RR or rr); also called pure  Heterozygous genotype - gene combination of one dominant & one recessive allele (e.g. Rr); also called hybrid copyright cmassengale

19. 18 Genes and Environment Determine Characteristics copyright cmassengale

20. 19 Mendel’s Pea Plant Experiments copyright cmassengale

21. 20 Why peas, Pisum sativum?  Can be grown in a small area  Produce lots of offspring  Produce pure plants when allowed to self-pollinate several generations  Can be artificially cross-pollinated copyright cmassengale

22. 21 Reproduction in Flowering Plants Pollen contains sperm Produced by the stamen Ovary contains eggs Found inside the flower Pollen carries sperm to the eggs for fertilization Self-fertilization can occur in the same flower Cross-fertilization can occur between flowers copyright cmassengale

23. 22 Mendel’s Experimental Methods Mendel hand-pollinated flowers using a paintbrush He could snip the stamens to prevent self-pollination Covered each flower with a cloth bag He traced traits through the several generations copyright cmassengale

24. 23 How Mendel Began Mendel produced pure strains by allowing the plants to self- pollinate for several generations copyright cmassengale

25. 24 Eight Pea Plant Traits Seed shape --- Round (R) or Wrinkled (r) Seed Color ---- Yellow (Y) or Green ( y ) Pod Shape --- Smooth (S) or wrinkled ( s ) Pod Color --- Green (G) or Yellow (g) Seed Coat Color ---Gray (G) or White (g) Flower position---Axial (A) or Terminal (a) Plant Height --- Tall (T) or Short (t) Flower color --- Purple (P) or white ( p ) copyright cmassengale

26. 25copyright cmassengale

27. 26copyright cmassengale

28. 27 Mendel’s Experimental Results copyright cmassengale

29. 28 Did the observed ratio match the theoretical ratio? The theoretical or expected ratio of plants producing round or wrinkled seeds is 3 round :1 wrinkled Mendel’s observed ratio was 2.96:1 The discrepancy is due to statistical error The larger the sample the more nearly the results approximate to the theoretical ratio copyright cmassengale

30. 29 Generation “Gap” Parental P 1 Generation = the parental generation in a breeding experiment. F 1 generation = the first-generation offspring in a breeding experiment. (1st filial generation) From breeding individuals from the P 1 generation F 2 generation = the second-generation offspring in a breeding experiment. (2nd filial generation) From breeding individuals from the F 1 generation From breeding individuals from the F 1 generation copyright cmassengale

31. 30 Following the Generations Cross 2 Pure Plants TT x tt Results in all Hybrids Tt Cross 2 Hybrids get 3 Tall & 1 Short TT, Tt, tt copyright cmassengale

32. 31 Monohybrid Crosses copyright cmassengale

33. 32 Trait: Seed Shape Alleles: R – Roundr – Wrinkled Cross: Round seeds x Wrinkled seeds RR x rr P 1 Monohybrid Cross R R rr Rr Genotype:Rr Genotype: Rr PhenotypeRound Phenotype: Round Genotypic Ratio:All alike Genotypic Ratio: All alike Phenotypic Ratio: All alike copyright cmassengale

34. 33 P 1 Monohybrid Cross Review  Homozygous dominant x Homozygous recessive  Offspring all Heterozygous (hybrids)  Offspring called F 1 generation  Genotypic & Phenotypic ratio is ALL ALIKE copyright cmassengale

35. 34 Trait: Seed Shape Alleles: R – Roundr – Wrinkled Cross: Round seeds x Round seeds Rr x Rr F 1 Monohybrid Cross R r rR RR rrRr Genotype:RR, Rr, rr Genotype: RR, Rr, rr PhenotypeRound & wrinkled Phenotype: Round & wrinkled G.Ratio:1:2:1 G.Ratio: 1:2:1 P.Ratio: 3:1 copyright cmassengale

36. 35 F 1 Monohybrid Cross Review  Heterozygous x heterozygous  Offspring: 25% Homozygous dominant RR 50% Heterozygous Rr 25% Homozygous Recessive rr  Offspring called F 2 generation  Genotypic ratio is 1:2:1  Phenotypic Ratio is 3:1 copyright cmassengale

37. 36 What Do the Peas Look Like? copyright cmassengale

38. 37 …And Now the Test Cross Mendel then crossed a pure & a hybrid from his F 2 generation This is known as an F 2 or test cross There are two possible testcrosses: Homozygous dominant x Hybrid Homozygous recessive x Hybrid copyright cmassengale

39. 38 Trait: Seed Shape Alleles: R – Roundr – Wrinkled Cross: Round seeds x Round seeds RR x Rr F 2 Monohybrid Cross (1 st ) R R rR RR RrRR Rr Genotype:RR, Rr Genotype: RR, Rr PhenotypeRound Phenotype: Round Genotypic Ratio:1:1 Genotypic Ratio: 1:1 Phenotypic Ratio: All alike copyright cmassengale

40. 39 Trait: Seed Shape Alleles: R – Roundr – Wrinkled Cross: Wrinkled seeds x Round seeds rr x Rr F 2 Monohybrid Cross (2nd) r r rR Rr rrRr rr Genotype:Rr, rr Genotype: Rr, rr PhenotypeRound & Wrinkled Phenotype: Round & Wrinkled G. Ratio:1:1 G. Ratio: 1:1 P.Ratio: 1:1 copyright cmassengale

41. 40 F 2 Monohybrid Cross Review  Homozygous x heterozygous(hybrid)  Offspring: 50% Homozygous RR or rr 50% Heterozygous Rr  Phenotypic Ratio is 1:1  Called Test Cross because the offspring have SAME genotype as parents copyright cmassengale

42. 41 Practice Your Crosses Work the P 1, F 1, and both F 2 Crosses for each of the other Seven Pea Plant Traits copyright cmassengale

43. 42 Mendel’s Laws copyright cmassengale

44. 43 Results of Monohybrid Crosses Inheritable factors or genes are responsible for all heritable characteristics Phenotype is based on Genotype Each trait is based on two genes, one from the mother and the other from the father True-breeding individuals are homozygous ( both alleles) are the same copyright cmassengale

45. 44 Law of Dominance In a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation. All the offspring will be heterozygous and express only the dominant trait. RR x rr yields all Rr (round seeds) copyright cmassengale

46. 45 Law of Dominance copyright cmassengale

47. 46 Law of Segregation During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other. Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring. copyright cmassengale

48. 47 Applying the Law of Segregation copyright cmassengale

49. 48 Law of Independent Assortment Alleles for different traits are distributed to sex cells (& offspring) independently of one another. This law can be illustrated using dihybrid crosses. copyright cmassengale

50. 49 Dihybrid Cross A breeding experiment that tracks the inheritance of two traits. Mendel’s “Law of Independent Assortment” a. Each pair of alleles segregates independently during gamete formation b. Formula: 2 n (n = # of heterozygotes) copyright cmassengale

51. 50 Question: How many gametes will be produced for the following allele arrangements? Remember: 2 n (n = # of heterozygotes) 1.RrYy 2.AaBbCCDd 3.MmNnOoPPQQRrssTtQq copyright cmassengale

52. 51 Answer: 1. RrYy: 2 n = 2 2 = 4 gametes RY Ry rY ry 2. AaBbCCDd: 2 n = 2 3 = 8 gametes ABCD ABCd AbCD AbCd aBCD aBCd abCD abCD 3. MmNnOoPPQQRrssTtQq: 2 n = 2 6 = 64 gametes copyright cmassengale

53. 52 Dihybrid Cross Traits: Seed shape & Seed color Alleles: Alleles: R round r wrinkled Y yellow y green RrYy x RrYy RY Ry rY ry All possible gamete combinations copyright cmassengale

54. 53 Dihybrid Cross RYRyrYry RYRy rY ry copyright cmassengale

55. 54 Dihybrid Cross RRYY RRYy RrYY RrYy RRYy RRyy RrYy Rryy RrYY RrYy rrYY rrYy RrYy Rryy rrYy rryy Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1 9:3:3:1 phenotypic ratio RYRyrYryRY Ry rY ry copyright cmassengale

56. 55 Dihybrid Cross Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1 9:3:3:1 copyright cmassengale

57. 56 Test Cross A mating between an individual of unknown genotype and a homozygous recessive individual. Example: bbC__ x bbcc BB = brown eyes Bb = brown eyes bb = blue eyes CC = curly hair Cc = curly hair cc = straight hair bCb___bc copyright cmassengale

58. 57 Test Cross Possible results: bCb___bcbbCc CbCb___bc bbccor c copyright cmassengale

59. 58 Summary of Mendel’s laws LAW PARENT CROSS OFFSPRING DOMINANCE TT x tt tall x short 100% Tt tall SEGREGATION Tt x Tt tall x tall 75% tall 25% short INDEPENDENT ASSORTMENT RrGg x RrGg round & green x round & green 9/16 round seeds & green pods 3/16 round seeds & yellow pods 3/16 wrinkled seeds & green pods 1/16 wrinkled seeds & yellow pods copyright cmassengale

60. Single-gene Inheritance in Humans 1. A Mendelian trait is caused by a single gene. 2. Mendelian human conditions are considered more rare than multifactorial ones 3. Mendelian inheritance in humans is more complex than in model organisms such as pea plants. copyright cmassengale59

61. Eye color The inheritance of eye color is an example of a single gene trait copyright cmassengale60

62. Modes of Inheritance Modes of inheritance – rules explaining common patterns of inheritance Genes may be autosomal or on a sex chromosome Alleles can be dominant or recessvie copyright cmassengale61

63. copyright cmassengale62

64. Criteria for an autosomal dominant trait: 1. Males & females can be affected; male to male transmission can occur 2. Both transmit the trait with equal frequency 3. Successive generations are affected. 4. Transmission stops after a generation where no one is affected. copyright cmassengale63

65. Criteria for an autosomal recessive trait 1. Males & females can be affected 2. Both can transmit the gene, unless it causes death before reproductive age 3. The trait can skip generations 4. Parents of an affected individual are heterozygous or have the trait. copyright cmassengale64

66. Modes of inheritance, cont. 1. Blood relatives that have children together have a much higher risk of having a child with a rare recessive disorder. 2. Marriage between relatives introduces consanguinity, literally meaning “shared blood” However genes are not passed in blood 3. Punnett squares apply Mendel’s first law to predict recurrence risks of inherited disorders or traits. 4. A Mendelian trait applies anew to each child. copyright cmassengale65

67. On the Meaning of Dominance & Recessiveness At the biochemical level, recessive disorders often result from alleles that cause a loss of function or loss of a normal protein Dominant disorders can result from production of an abnormal protein that interferes with the function of a normal protein or imparts a gain of function. copyright cmassengale66

68. Recessive disorders Recessive orders tend to be more severe producing symptoms earlier than dominant disorders Disease causing recessive alleles remain in populations because heterozygotes pass them to future generations. copyright cmassengale67

69. Dominant disorders If a dominant mutation that harms early in life arises people who have the allele are too ill or don’t survive long enough to reproduce The allele becomes rare in the population unless it arises anew by mutation Dominant disorders that do not appear until adulthood or drastically disrupt health, remain in the population until after a person has reproduced. copyright cmassengale68

70. Pedigree Analysis Pedigree charts depict family relationships and transmission of inherited traits. Squares represent males and circles represent females. Horizontal lines indicate parents, vertical lines show generations, and elevated lines depict siblings. Symbols for heterozygotes are half-shaded, and for an individual with a particular phenotype, completely shaded copyright cmassengale69

71. copyright cmassengale70

72. Pedigrees Then and Now Pedigrees have been in use since antiquity. They have been used throughout history to show family relationships, particularly royal bloodlines. copyright cmassengale71

73. copyright cmassengale72

74. Pedigrees Display Mendel’s Laws Pedigrees can reveal mode of inheritance, and can suggest molecular information, carrier status, and input from other genes and the environment. Interpretation of pedigrees can be inconclusive when more than one mode of inheritance can explain the pattern seen. copyright cmassengale73

75. Solving Genetics Problems  List genotypes and phenotypes for the trait  Determine the genotypes of the parents  Possible gametes  Possible genotypes of offspring  Repeat for successive generations

76. Independent Events The probability of simultaneous independent events = the product of the probability of each event Example: If both parents are heterozygous (Bb)) what is the probability that they will produce a BB child? Probability of a sperm with B allele = ½ Probability of a ova with B allele = ½ Probability of a BB child is ½ X ½ = ¼

77. Dependent Events The probability of dependent events = the sum of probability of each event Example Parents are heterozygous for a trait, R. What is the chance that their child carries at least one dominant R allele? Probability of child carrying RR = ¼ Probability of child carrying Rr = ½ Probability of child carrying R_ = ¼ + ½ = ¾