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Sylvia S. Mader Copyright © The McGraw Hill Companies Inc. Permission required for reproduction or display PowerPoint® Lecture Slides are prepared by Dr.

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Presentation on theme: "Sylvia S. Mader Copyright © The McGraw Hill Companies Inc. Permission required for reproduction or display PowerPoint® Lecture Slides are prepared by Dr."— Presentation transcript:

1 Sylvia S. Mader Copyright © The McGraw Hill Companies Inc. Permission required for reproduction or display PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor BIOLOGY 10th Edition Mendelian Patterns of Inheritance Chapter 11: pp Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Parents eggs Ee spem Punnett square Offspring Ee E e Ee EE ee TTtt t T Tt eggs sperm Offspring Tt T t TT Tt tt

2 2 Blending Inheritance Theories of inheritance in Mendel’s time: Based on blending Parents of contrasting appearance produce offspring of intermediate appearance

3 3 Gregor Mendel Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. © Ned M. Seidler/Nationa1 Geographic Image Collection Mendel’s findings were in contrast with this Particulate theory of inheritance Involves reshuffling of genes from generation to generation

4 4 Law of Segregation Each individual has a pair of alleles for each trait The alleles segregate (separate) during gamete formation Each gamete contains only one allele from each pair Fertilization gives the offspring two factors for each trait

5 5 Mendel’s Monohybrid Crosses: An Example Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. TTtt t T P generation P gametes F 1 gametes F 2 generation F 1 generation Tt Tt sperm T t TTTt tt Offspring Phenotypic Ratio short 1 tall 3 Allele Key T = tall plant t = short plant

6 6 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

7 7 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.

8 8 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

9 9 Genotype versus Phenotype

10 10 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

11 11 Punnett Square Can 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 =½x½=¼ The chance of Ee =½x½=¼ The chance of eE =½x½=¼ The chance of ee =½x½=¼

12 12 Punnett Square Showing Earlobe Inheritance Patterns Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Parents Ee eggs spem Punnett square Offspring Ee E e Ee EE ee Allele keyPhenotypic Ratio unattached earlobes 3 1 E = unattached earlobes e = attached earlobes attached earlobes

13 13 Monohybrid Test cross Test cross determines genotype of individual having dominant phenotype Based on the knowledge that individuals with recessive phenotype always known homozygous recessive genotype

14 Monohybrid Test cross However, individuals with dominant phenotype have unknown genotype May be homozygous dominant, or Heterozygous 14

15 15 Two-Trait Inheritance Dihybrid cross uses true-breeding plants differing in two traits Observed phenotypes among F 2

16 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 16

17 Animation 17 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

18 Sample Dihybrid Problem Tall is dominant to short and purple is dominant to white in pea plants. Cross two plants that are heterozygous for both traits. 18

19 Chi-Square Chi-Square Tutorial In the garden pea, yellow cotyledon color is dominant to green, and inflated pod shape is dominant to the constricted form. Considering both of these traits jointly in self-fertilized dihybrids, the progeny appeared in the following numbers: 193 green, inflated; 184 yellow constricted 556 yellow, inflated; 61 green, constricted Do these genes assort independently? Support your answer using Chi-square analysis. 19

20 Gene Linkage 1. How are the scientists results different from Mendel’s work? 2. How did they explore their results? 3. How did the scientists explain their findings? Genetic linkage is very strong for genes which are located close to each other on the same chromosome. What happens in the case of two genes which are far apart on the same chromosome? 20

21 Are all alleles completely dominant or recessive? Incomplete Dominance The heterozygous is in between the homozygous individuals. Phenotype reveals genotype without test cross 21

22 Example Cross two pink flowers. What genotypes and phenotypes are possible? 22

23 Co-Dominant Both alleles are expressed in the phenotype. 23

24 Example In humans blood type AB (I A I B ) is codominant. What blood types are possible if two people with AB blood type have children? 24

25 Do any genes have more than two alleles? Multiple Alleles The gene has several allelic forms But each individual still receives two 25

26 Practice Mom is Type A and Dad is Type B, what are all the possible blood types for their children? 26

27 Is each phenotypic trait influenced by only one gene? Polygenic 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 27

28 28

29 For genes that are on the X chromosome in humans and other mammals, what are the differences in inheritance for males vs. females? 29

30 30 X – Linked Inheritance In mammals The X and Y chromosomes determine gender Females = XX Males = XY

31 X-linked = genes that have nothing to do with gender Carried on the X chromosome and the Y does not have these genes. Discovered in the early 1900s by a group at Columbia University, headed by Thomas Hunt Morgan. 31

32 32 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.

33 Practice Cross a male hemophiliac with a female whose father was a hemophiliac. What are the possible genotypes and phenotypes of their children? 33

34 Human Genetic Disorders/Pedigrees Autosomal – any gene not on the sex chromosomes Dominant genetic disorder (brittle bone) AA and Aa have the disorder Recessive genetic disorder (cystic fibrosis) aa has the disorder 34

35 35 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 A? Aa * aa A? Key aa = affected Aa = carrier (unaffected) AA = unaffected A? = unaffected (one allele unknown) I II III IV

36 36 Autosomal Dominant Pedigree Chart 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.

37 37 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

38 38 Methemoglobinemia Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Courtesy Division of Medical Toxicology, University of Virginia

39 39 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

40 40 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

41 41 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 SkeletonSkinLungsEyes 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

42 X-Linked Recessive Pedigree 42 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.

43 43 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

44 44 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)

45 45 Review Blending Inheritance Monohybrid Cross Law of Segregation Modern Genetics Genotype vs. Phenotype Punnett Square Dihybrid Cross Law of Independent Assortment Human Genetic Disorders

46 Sylvia S. Mader Copyright © The McGraw Hill Companies Inc. Permission required for reproduction or display PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor BIOLOGY 10th Edition Mendelian Patterns of Inheritance Chapter 11: pp Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Parents eggs Ee spem Punnett square Offspring Ee E e Ee EE ee TTtt t T Tt eggs sperm Offspring Tt T t TT Tt tt


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