The document summarizes key concepts in genetics discovered by Gregor Mendel through his experiments with pea plants, including: - Mendel performed breeding experiments with pea plants and discovered the laws of segregation and independent assortment. - He found that traits are passed from parents to offspring through discrete factors (now known as genes and alleles) that sort independently during gamete formation and fertilization. - Mendel's work laid the foundation for modern genetics concepts such as genotypes, phenotypes, dominance, and the use of Punnett squares to predict offspring ratios. - The document also discusses how Mendel's principles can be applied to understand human genetic disorders and inheritance patterns such as autosomal and

1. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Parents eggs Ee Ee spem Punnett square Offspring E e E e Ee Ee EE ee TT tt t T Tt eggs sperm Offspring T t T t TT Tt Tt tt

2. Outline Blending Inheritance Monohybrid Cross Law of Segregation Modern Genetics Genotype vs. Phenotype Punnett Square Dihybrid Cross Law of Independent Assortment Human Genetic Disorders

3. Gregor Mendel Austrian monk Studied science and mathematics at 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 early 1860s Had no knowledge of cells or chromosomes Did not have a microscope

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

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

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

7. Blending Inheritance Theories of inheritance in Mendel’s time: Based on blending Parents of contrasting appearance produce offspring of intermediate appearance Mendel’s findings were in contrast with this He formulated the particulate theory of inheritance Inheritance involves reshuffling of genes from generation to generation

8. One-Trait Inheritance 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

9. Mendel’s Monohybrid Crosses: An Example Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. TT tt t T P generation P gametes F 1 gametes F 2 generation F 1 generation Tt T t sperm T t TT Tt Tt tt Offspring Phenotypic Ratio short 1 tall 3 Allele Key T = tall plant t = short plant

10. 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 Fertilization gives the offspring two factors for each trait

11. Modern Genetics View 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

12. Homologous Chromosomes 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.

13. Genotype versus Phenotype 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

14. Genotype versus Phenotype

15. 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

16. 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

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

18. Monohybrid Test cross Individuals with recessive phenotype always have the homozygous recessive genotype However, individuals with dominant phenotype have indeterminate genotype May be homozygous dominant, or Heterozygous Test cross determines genotype of individual having dominant phenotype

19. One-Trait Test Cross Insert figure 11.7a here Phenotypic Ratio eggs a. sperm t T t Offspring Tt tt Tt tt Allele Key short 1 tall 1 T = tall plant t = short plant Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

20. One-Trait Test Cross Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. b. t T Tt Offspring eggs sperm TT tt Allele Key Phenotypic Ratio All tall plants T = tall plant t = short plant

21. Two-Trait Inheritance Dihybrid cross uses true-breeding plants differing in two traits Observed phenotypes among F 2 plants Formulated 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 Mendel tracked each trait through two generations. P generation is the parental generation in a breeding experiment. F1 generation is the first-generation offspring in a breeding experiment. F2 generation is the second-generation offspring in a breeding experiment

22. Two-Trait (Dihybrid) Cross Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. TtGg ttgg TTGG Offspring P generation P gametes F 2 generation F 1 generation F 1 gametes eggs sperm TG Tg TG Tg tg tG tG tg tg TG TTGg TtGG TtGg TTGg Ttgg TtGG ttGG ttGg TtGg Ttgg ttGg ttgg TTGG TtGg TTgg TtGg Allele Key = = = = T t G g tall plant short plant green pod yellow pod Phenotypic Ratio 9 tall plant, green pod 3 tall plant, yellow pod 3 short plant, green pod 1 short plant, yellow pod

23. Independent Assortment and Segregation during Meiosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Parent cell has two pairs of homologous chromosomes. All possible combina- 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 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. A A A A A A A AB ab Ab aB a a a a a a a A A b A a a a B B B B B B B B B B a B b b b A A b b B B a a b b b b b A b b either or

24. Animation 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.

25. Human Genetic Disorders 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 disorder Other genetic disorders are autosomal recessive An individual with AA does NOT have disorder An individual with Aa does NOT have disorder, but is a carrier An individual with aa DOES have the disorder

26. Autosomal Recessive Pedigree Chart Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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. aa aa Aa Aa Aa A? A? A? Aa * aa A? A? A? Key aa = affected Aa = carrier (unaffected) AA = unaffected A? = unaffected (one allele unknown) I II III IV

27. Autosomal Dominant Pedigree Chart Aa aa aa aa aa aa aa aa Aa aa Aa Aa A? Aa Autosomal dominant disorders 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. * I II III • Key AA = affected Aa = affected A? = affected (one allele unknown) aa = unaffected Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

28. Autosomal Recessive Disorders Tay-Sachs Disease Progressive deterioration of psychomotor functions Cystic Fibrosis Mucus in bronchial tubes and pancreatic ducts is particularly thick and viscous Phenylketonuria (PKU) Lack enzyme for normal metabolism of phenylalanine

29. Cystic Fibrosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cl - H 2 O H 2 O H 2 O Cl - Cl - Cl - Cl - thick mucus defective channel nebulizer percussion vest © Pat Pendarvis

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

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32. Autosomal Dominant Disorders Neurofibromatosis Tan or dark spots develop on skin and darken Small, benign tumors may arise from fibrous nerve coverings Huntington Disease Neurological disorder Progressive degeneration of brain cells Severe muscle spasms Personality disorders

33. A Victim of Huntington Disease Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a: © Steve Uzzell JJ JK JK JK JK JJ K L JK JK JK JK K L JK JK K L KK K L J L JJ J L JK J L K L KL J L J L J L J L JJ K L JJ K L JJ K L K L a. b.

34. Incomplete Dominance Heterozygote has 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 test cross

35. Incomplete Dominance 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

36. Multiple Allelic Traits Some traits controlled by multiple alleles The gene exists in several allelic forms (but each individual only has two) ABO blood types The alleles: I A = A antigen on red cells, anti-B antibody in plasma I B = B antigen on red cells, anti-AB antibody in plasma I = Neither A nor B antigens, both antibodies

37. Multiple Allelic Traits

38. Pleioptropic Effects Pleiotropy occurs when a single mutant gene affects two or more distinct and seemingly unrelated traits. Marfan syndrome have disproportionately long arms, legs, hands, and feet; a weakened aorta; poor eyesight

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

40. 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 Result in continuous variation of phenotypes

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

42. X – Linked Inheritance In mammals The X and Y chromosomes determine gender Females are XX Males are XY The term X-linked is used for genes that have nothing to do with gender 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

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

44. Human X-Linked Disorders 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. Muscular dystrophy Wasting away of the muscle 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 a clotting factor VIII, or clotting factor IX Affected person’s blood either does not clot or clots very slowly.

45. X-Linked Recessive Pedigree Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. X B X B X b Y grandfather daughter X B X b X B Y X B Y X b X b X b Y X B X b grandson X B Y X B X B X b Y 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.

46. Muscle Dystrophy 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

47. Terminology Pleiotropy A gene that affects more than one characteristic of an individual Sickle-cell (incomplete dominance) Codominance More than one allele is fully expressed ABO blood type (multiple allelic traits) Epistasis A gene at one locus interferes with the expression of a gene at a different locus Human skin color (polygenic inheritance)

48. Review Blending Inheritance Monohybrid Cross Law of Segregation Modern Genetics Genotype vs. Phenotype Punnett Square Dihybrid Cross Law of Independent Assortment Human Genetic Disorders

49. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Parents eggs Ee Ee spem Punnett square Offspring E e E e Ee Ee EE ee TT tt t T Tt eggs sperm Offspring T t T t TT Tt Tt tt