Biology, 9th ed,Sylvia Mader Chapter 11 1 Mendelian Inheritance Biology Sylvia S. Mader Michael Windelspecht Chapter 11 Mendelian Patterns of Inheritance Lecture Outline See separate FlexArt PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes. 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Outline • 11.1 Gregor Mendel • 11.2 Mendel s Laws • 11.3 Extending the Range of Mendelian Genetics 2 Biology, 9th ed,Sylvia Mader Chapter 11 2 Mendelian Inheritance 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 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 Biology, 9th ed,Sylvia Mader Chapter 11 3 Mendelian Inheritance Gregor Mendel Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. © Ned M. Seidler/Nationa1 Geographic Image Collection 5 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 6 Biology, 9th ed,Sylvia Mader Chapter 11 4 Mendelian Inheritance Garden Pea Anatomy Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Flower Structure stamen anther filament stigma style ovules in ovary carpel a. 7 Garden Pea Anatomy 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. 8 Biology, 9th ed,Sylvia Mader Chapter 11 5 Mendelian Inheritance Garden Pea Anatomy Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Trait Stem length Characteristics *Dominant *Recessive Tall Short Pod shape Inflated Constricted Seed shape Round Wrinkled Seed color Yellow Green Flower position Axial Terminal Flower color Purple White Pod color Green Yellow b. 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 = F1 • Second filial generation offspring = F2 Formulated the Law of Segregation 10 Biology, 9th ed,Sylvia Mader Chapter 11 6 Mendelian Inheritance Monohybrid Cross done by Mendel Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Allele Key T = tall plant t = short plant Phenotypic Ratio 3 1 tall short TT tt 11 Monohybrid Cross done by Mendel Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Allele Key T = tall plant t = short plant Phenotypic Ratio 3 1 tall short P generation TT tt 12 Biology, 9th ed,Sylvia Mader Chapter 11 7 Mendelian Inheritance Monohybrid Cross done by Mendel Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Allele Key T = tall plant t = short plant Phenotypic Ratio 3 tall 1 short P generation TT P gametes tt T t 13 Monohybrid Cross done by Mendel Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Allele Key T = tall plant t = short plant Phenotypic Ratio 3 tall 1 short P generation TT P gametes tt T tt t F1 generation Tt 14 Biology, 9th ed,Sylvia Mader Chapter 11 8 Mendelian Inheritance Monohybrid Cross done by Mendel Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Allele Key Phenotypic Ratio T = tall plant t = short plant 3 1 P generation TT tall short P gametes tt t T F1 generation Tt eggs F1 gametes T t sperm T t 15 Monohybrid Cross done by Mendel Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. P generation T = tall plant t = short plant Phenotypic Ratio 3 1 TT tall short P gametes tt t T F1 generation Tt eggs F1 gametes T t T sperm Allele Key TT t 16 Biology, 9th ed,Sylvia Mader Chapter 11 9 Mendelian Inheritance Monohybrid Cross done by Mendel Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. F1 generation Allele key Phenotypic Ratio T = tall plant t = short plant 3 1 TT tt tall short t T P gametes F1 generation Tt eggs F1 gametes T t sperm T TT Tt t 17 Monohybrid Cross done by Mendel Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. P generation T = tall plant t = short plant Phenotypic Ratio 3 tall 1 short TT P gametes tt t T F1 generation Tt eggs T F1 gametes t T sperm Allele Key TT Tt t Tt 18 Biology, 9th ed,Sylvia Mader Chapter 11 10 Mendelian Inheritance Monohybrid Cross done by Mendel Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. P generation TT tt t T P gametes F1 generation Tt eggs F1 gametes T t F2 generation sperm T TT Tt Tt tt t Offspring Allele Key T = tall plant t = short plant Phenotypic Ratio 3 1 tall short 19 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 Biology, 9th ed,Sylvia Mader Chapter 11 11 Mendelian Inheritance 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 Classical View of Homologous Chromosomes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. sister chromatids alleles at a gene locus a. Homologous chromosomes have alleles for same genes at specific loci. G g R r S s t T G Replication b. Sister chromatids of duplicated chromosomes have same alleles for each gene. R G g g R r r S S s s t t T T 22 Biology, 9th ed,Sylvia Mader Chapter 11 12 Mendelian Inheritance Relationship Between Observed Phenotype and F2 Offspring Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Trait Dominant F2Results Characteristics Recessive Dominant Recessive Ratio Tall Short 787 277 2.84:1 Pod shape Inflated Constricted 882 299 2.95:1 Seed shape Round Wrinkled 5,474 1,850 2.96:1 Seed color Yellow Green 6,022 2,001 3.01:1 Axial Terminal 651 207 3.14:1 Flower color Purple White 705 224 3.15:1 Pod color Green Yellow 428 152 2.82:1 14,949 5,010 2.98:1 Stem length Flower position Totals: 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 Biology, 9th ed,Sylvia Mader Chapter 11 13 Mendelian Inheritance 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 F1 plants showed both dominant characteristics F1 plants self-pollinated Observed phenotypes among F2 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. • F1 generation is the first-generation offspring in a breeding experiment. • F2 generation is the second-generation offspring in a breeding experiment 25 Dihybrid Cross Done by Mendel Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. × P generation TTGG P gametes ttgg tg TG F1 generation TtGg eggs TG F1 gametes Tg tG tg TG TTGg TtGG TtGg TTGg TTgg TtGg Ttgg TtGG TtGg ttGG ttGg Ttgg ttGg ttgg Tg sperm F2 generation TTGG tG tg TtGg Offspring Allele Key T t G g = = = = tall plant short plant green pod Yellow pod 9 3 3 1 Phenotypic Ratio tall plant, green pod tall plant, yellow pod short plant, green pod short plant, yellow pod Biology, 9th ed,Sylvia Mader Chapter 11 14 Mendelian Inheritance Independent Assortment and Segregation during Meiosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. A a B b Parent cell has two pairs of homologous chromosomes. 27 Independent Assortment and Segregation during Meiosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. A Aa a B Bb b er th ei A a B b Parent cell has two pairs of homologous chromosomes. 28 Biology, 9th ed,Sylvia Mader Chapter 11 15 Mendelian Inheritance Independent Assortment and Segregation during Meiosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. A Aa a B Bb b A Aa a b bB B er th ei A a B b or Parent cell has two pairs of homologous chromosomes. 29 Independent Assortment and Segregation during Meiosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. A Aa a B Bb b A Aa a b bB B er th ei A a B b or Parent cell has two pairs of homologous chromosomes. All orientations of homologous chromosomes are possible at metaphase I in keeping with the law of independent assortment. 30 Biology, 9th ed,Sylvia Mader Chapter 11 16 Mendelian Inheritance Independent Assortment and Segregation during Meiosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. A Aa a B Bb b er th ei A A A B B a a b b a B b or Parent cell has two pairs of homologous chromosomes. A Aa b bB B a All orientations of homologous chromosomes are possible at metaphase I in keeping with the law of independent assortment. 31 Independent Assortment and Segregation during Meiosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. A Aa a B Bb b er th ei A A A B B a a b b A A b b a B b or Parent cell has two pairs of homologous chromosomes. A Aa a b bB B All orientations of homologous chromosomes are possible at metaphase I in keeping with the law of independent assortment. a a B B 32 Biology, 9th ed,Sylvia Mader Chapter 11 17 Mendelian Inheritance Independent Assortment and Segregation during Meiosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. A A B B A Aa a B Bb b a a e A b er ith b a B b A A or b b Parent cell has two pairs of homologous chromosomes. A Aa a b bB B a a B B All orientations of homologous 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 33 Independent Assortment and Segregation during Meiosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. A A Aa a B Bb b er th ei A A A B B B AB A B a a a b b b ab a b a B b or A A b b A Ab A Parent cell has two pairs of homologous chromosomes. A Aa a b bB B a a B B b a b B aB a All orientations of homologous 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 B All possible combi tions of chromosomes and alleles occur in the gametes as suggested by Mendel's two laws. 34 Biology, 9th ed,Sylvia Mader Chapter 11 18 Mendelian Inheritance 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 35 the squares 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 36 Biology, 9th ed,Sylvia Mader Chapter 11 19 Mendelian Inheritance Punnett Square Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Parents Ee Ee eggs e spem E EE Ee Ee ee e Punnett square E Offspring Allele key E = unattached earlobes e = attached earlobes Phenotypic Ratio 3 1 unattached earlobes attached earlobes 37 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 38 Biology, 9th ed,Sylvia Mader Chapter 11 20 Mendelian Inheritance One-Trait Testcross 39 One-Trait Testcross Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. TT tt T t eggs sperm Tt b. Allele Key T = tall plant t = short plant Phenotypic Ratio All tall plants Offspring 40 Biology, 9th ed,Sylvia Mader Chapter 11 21 Mendelian Inheritance 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. 41 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 42 Biology, 9th ed,Sylvia Mader Chapter 11 22 Mendelian Inheritance Autosomal Recessive Pedigree Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Generations I aa II Aa A? III A? Aa IV Aa * A? Aa aa aa A? A? Key aa = affected Aa = carrier (unaffected) AA = unaffected A? = unaffected (one allele unknown) A? 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. 43 Autosomal Dominant Pedigree Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Generations Aa Aa I * II III Aa aa Aa Aa aa A? aa aa aa aa aa aa Key AA = affected Aa = affected Autosomal dominant disorders A? = affected (one allele unknown) • Affected children will usually have an aa = unaffected 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. 44 Biology, 9th ed,Sylvia Mader Chapter 11 23 Mendelian Inheritance 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 45 Methemoglobinemia Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Courtesy Division of Medical Toxicology, University of Virginia 46 Biology, 9th ed,Sylvia Mader Chapter 11 24 Mendelian Inheritance Cystic Fibrosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. H 2O Cl- Cl- ClCl- H 2O H 2O Cl- nebulizer defective channel percussion vest thick mucus © Pat Pendarvis 47 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 48 Biology, 9th ed,Sylvia Mader Chapter 11 25 Mendelian Inheritance 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: • IA = A antigen on red blood cells, anti-B antibody in plasma • IB = 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 antiB antibodies in plasma • The ABO blood type is also an example of codominance More than one allele is fully expressed Both IA and IB are expressed in the presence of the other 49 ABO Blood Type Phenotype A B AB O Genotype IAIA, IAi IBIB, IBi IAIB ii 50 Biology, 9th ed,Sylvia Mader Chapter 11 26 Mendelian Inheritance 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 51 Incomplete Dominance Copyright © The McGraw-Hill Companies, Inc. 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R1R2 R1R2 eggs R1 R2 sperm R1 R1R1 R1R2 R2 R1R2 Offspring R2R2 Key 1 R1R1 2 R1R2 1 R2R2 red pink white 52 Biology, 9th ed,Sylvia Mader Chapter 11 27 Mendelian Inheritance 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 53 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 54 Biology, 9th ed,Sylvia Mader Chapter 11 28 Mendelian Inheritance 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 55 Marfan Syndrome Copyright © The McGraw-Hill Companies, Inc. 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Connective tissue defects Skeleton Chest wall deformities Long, thin fingers, arms, legs Scoliosis (curvature of the spine) Flat feet Long, narrow face Loose joints Heart and blood vessels Mitral valve prolapse Enlargement of aorta Eyes Lens dislocation Severe nearsightedness Lungs Collapsed lungs Aneurysm Aortic wall tear Skin Stretch marks in skin Recurrent hernias Dural ectasia: stretching of the membrane that holds spinal fluid (Left): © AP/Wide World Photos; (Right): © Ed Reschke; (Sickled cells, p. 203): © Phototake, Inc./Alamy 56 Biology, 9th ed,Sylvia Mader Chapter 11 29 Mendelian Inheritance 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 57 Polygenic Inheritance Copyright © The McGraw-Hill Companies, Inc. 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P generation F1 generation F2 generation Proportion of Population 20 — 64 15 — 64 6 — 64 1 — 64 58 Genotype Examples Biology, 9th ed,Sylvia Mader Chapter 11 30 Mendelian Inheritance Extending the Range of Mendelian Genetics • X-Linked Inheritance In mammals • The X and Y chromosomes determine gender • Females are XX • Males are XY 59 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 60 Biology, 9th ed,Sylvia Mader Chapter 11 31 Mendelian Inheritance X – Linked Inheritance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. P generation XrY Xr P gametes XRXR Y XR F1 generation XRY XRXr eggs F1 gametes XR Xr F2 generation sperm XR XRXR XRXr XRY XrY Y Offspring Allele Key XR = red eyes Xr = white eyes Phenotypic Ratio females: all red-eyed males: 1 red-eyed white-eyed 1 X – Linked Inheritance 61 Biology, 9th ed,Sylvia Mader Chapter 11 32 Mendelian Inheritance 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. 63 X-Linked Recessive Pedigree Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. XbY XBXB XBY XBXb daughter grandfather XBY XbXb XbY XBY XBXB XBXb X-Linked Recessive Disorders XbY grandson XBXB XBXb XbXb XbY XbY Key = Unaffected female = Carrier female = Color-blind female = Unaffected male = Color-blind male • 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. 64 Biology, 9th ed,Sylvia Mader Chapter 11 33 Mendelian Inheritance Muscular Dystrophy Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. fibrous tissue abnormal muscle normal tissue (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. 65