2. Mendelian Patterns of Inheritance Ch. 11

3. How are characteristics inherited? The “blending” hypothesis: The “particulate” hypothesis:

4. Advantages of pea plants for genetic study: Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

5. True Breeding = Hybridization = P generation = F 1 generation = F 2 generation = produced from self- pollination of F1 generation Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

6. Mendel’s Model 1.Variation in traits are due to alternate versions of genes –Alleles –locus – where the gene is found on the chromosome 2.Organisms inherit two alleles for each trait –one allele from each parent May be identical - May be different -

7. 3. If the two alleles at a locus differ then: –the dominant allele – –the recessive allele - Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

8. Fig. 14-4 Allele for purple flowers Homologous pair of chromosomes Locus for flower-color gene Allele for white flowers

9. Fig. 14-3-3 EXPERIMENT P Generation (true-breeding parents) Purple flowers White flowers  F 1 Generation (hybrids) All plants had purple flowers F 2 Generation 705 purple-flowered plants 224 white-flowered plants

10. Why did the white flower color seem to disappear?

11. 4. Law of Segregation The two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

12. What is Segregation? Alleles separate during gamete formation. Copyright Pearson Prentice Hall

13. Fig. 14-5-3 P Generation Appearance: Genetic makeup: Gametes: Purple flowers White flowers PP P pp p F 1 Generation Gametes: Genetic makeup: Appearance: Purple flowers Pp P p 1/21/2 1/21/2 F 2 Generation Sperm Eggs P P PPPp p p pp 31

14. Fig. 14-6 Phenotype Purple 3 Genotype 1 White Ratio 3:1 (homozygous) (heterozygous) PP Pp pp Ratio 1:2:1 1 1 2

15. Terms Phenotype – Genotype – Heterozygous – Homozygous – –Dominant – –Recessive –

16. Test Cross How can you determine the genotype for flower color of a plant with purple flowers

17. More of Mendel’s Questions Does the segregation of one pair of alleles affect the segregation of another pair of alleles? Example in True Breeding Pea Seeds: X Must a round seed always be yellow? YYRRyyrr

18. Law of Independent Assortment each pair of alleles segregates independently of each other pair of alleles during gamete formation applies only to genes on different, non- homologous chromosomes Genes located near each other on the same chromosome tend to be inherited together Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

19. Fig. 14-8 EXPERIMENT RESULTS P Generation F 1 Generation Predictions Gametes Hypothesis of dependent assortment YYRRyyrr YR yr YyRr  Hypothesis of independent assortment or Predicted offspring of F 2 generation Sperm YR yr Yr YR yR Yr yR yr YR YYRR YyRr YYRr YyRR YYrr Yyrr yyRR yyRr yyrr Phenotypic ratio 3:1 Eggs Phenotypic ratio 9:3:3:1 1/21/2 1/21/2 1/21/2 1/21/2 1/41/4 yr 1/41/4 1/41/4 1/41/4 1/41/4 1/41/4 1/41/4 1/41/4 1/41/4 3/43/4 9 / 16 3 / 16 1 / 16 Phenotypic ratio approximately 9:3:3:1 31510810132

20. Independent Assortment and Segregation during Meiosis 19 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.

21. The laws of probability Mendel’s laws of segregation and independent assortment reflect the rules of probability tossing a coin 1 st toss does not impact 2 nd toss the alleles of one gene segregate into gametes independently of another gene’s alleles Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

22. The multiplication rule: –the probability that two or more independent events will occur together is the product of their individual probabilities The Multiplication and Addition Rules Applied to Monohybrid Crosses

23. Fig. 14-9 Rr  Segregation of alleles into eggs Sperm R R R R R R r r r r r r 1/21/2 1/21/2 1/21/2 1/21/2 Segregation of alleles into sperm Eggs 1/41/4 1/41/4 1/41/4 1/41/4

24. The addition rule –the probability that any one of two or more exclusive events will occur is calculated by adding together their individual probabilities –can be used to figure out the probability that an F 2 plant from a monohybrid cross will be heterozygous rather than homozygous dominant or homozygous recessive Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

25. Fig. 14-9 Rr  Segregation of alleles into eggs Sperm R R R R R R r r r r r r 1/21/2 1/21/2 1/21/2 1/21/2 Segregation of alleles into sperm Eggs 1/41/4 1/41/4 1/41/4 1/41/4 To find probability of a heterozygous F2: add ¼ + ¼ = ½

26. Rule of Multiplication What is the probability that the following cross will have the offspring listed below? TtPpYy x TTppYy Offspring: TTPpyy

27. Fig. 14-UN1 Using multiplication rule and addition rule: Example: PpYyRr x Ppyyrr What will be the probability of at least 2 recessive traits in the F1 generation? 1 st determine which genotypes fulfill this condition (each must have at least 2 recessive traits)

28. Genetic Disorders Autosome - Genetic disorders caused by genes on autosomes are called autosomal disorders –Some genetic disorders are autosomal dominant –Other genetic disorders are autosomal recessive 27

29. Autosomal Recessive Pedigree 28 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)

30. Autosomal Dominant Pedigree 29 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

31. 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 30

32. Methemoglobinemia 31 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Courtesy Division of Medical Toxicology, University of Virginia

33. Cystic Fibrosis 32 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

34. loss of one amino acid delta F508

35. Sickle cell anemia (recessive) Primarily Africans –when oxygen levels are low, sickle-cell hemoglobin crystallizes into long rods deforms red blood cells into sickle shape sickling creates pleiotropic effects = cascade of other symptoms

37. Sickle cell anemia Substitution of one amino acid in polypeptide chain hydrophilic amino acid hydrophobic amino acid

38. Sickle cell phenotype The normal allele is incompletely dominant to the sickle-cell allele –both normal & mutant hemoglobins are synthesized in heterozygote (Aa) –50% cells sickle; 50% cells normal –carriers usually healthy –sickle-cell disease triggered under blood oxygen stress exercise

39. Heterozygote advantage Malaria –single-cell eukaryote parasite spends part of its life cycle in red blood cells In tropical Africa, where malaria is common: –homozygous dominant individuals die of malaria –homozygous recessive individuals die of sickle cell anemia –heterozygote carriers are relatively free of both reproductive advantage

40. Huntington’s chorea (dominant) Dominant inheritance –repeated mutation on end of chromosome 4 mutation = CAG repeats glutamine amino acid repeats in protein one of 1 st genes to be identified –build up of “huntington” protein in brain causing cell death memory loss muscle tremors, jerky movements –“chorea” starts at age 30-50 early death –10-20 years after start 1872

41. 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 type The ABO blood type is also an example of codominance –AB blood type 40

42. ABO Blood Type 41 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

43. Extending the Range of Mendelian Genetics Incomplete Dominance: –Heterozygote has a phenotype intermediate between that of either homozygote –Phenotype reveals genotype without a test cross 42

44. Incomplete dominance Heterozygote shows an intermediate, blended phenotype –example: RR = red flowers WW = white flowers RW = pink flowers RRWWRW

45. 44 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

46. 45 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

47. 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 46

48. Marfan Syndrome 47 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

49. 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 48

50. Polygenic Inheritance 49 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

51. Epistasis B_C_ bbC_ _ _cc One gene completely masks another gene –coat color in mice = 2 separate genes C,c: pigment (C) or no pigment (c) B,b: more pigment (black=B) or less (brown=b) cc = albino, no matter B allele 9:3:3:1 becomes 9:3:4

52. Epistasis in Labrador retrievers 2 genes: (E,e) & (B,b) –pigment (E) or no pigment (e) –pigment concentration: black (B) to brown (b) E–B–E–bbeeB–eebb

53. 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 52

54. X – Linked Inheritance 53 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

55. 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. 54

56. X-Linked Recessive Pedigree 55 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.

57. Muscular Dystrophy 56 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

58. Frequency of Dominant Alleles Dominant alleles are not necessarily more common in populations than recessive alleles For example, one baby out of 400 in the United States is born with extra fingers or toes The allele for this unusual trait is dominant to the allele for the more common trait of five digits per appendage In this example, the recessive allele is far more prevalent than the population’s dominant allele

59. Environmental effects Phenotype is controlled by both environment & genes Color of Hydrangea flowers is influenced by soil pH Human skin color is influenced by both genetics & environmental conditions Coat color in arctic fox influenced by heat sensitive alleles

60. A phenotypes range is called the norm of reaction These are broadest in polygenic characters Such characters are called multifactorial because genetic and environmental factors collectively influence phenotype Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings