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Human Biology Sylvia S. Mader Michael Windelspecht Chapter 20 Patterns of Genetic Inheritance Lecture Outline Copyright © The McGraw-Hill Companies, Inc.

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Presentation on theme: "Human Biology Sylvia S. Mader Michael Windelspecht Chapter 20 Patterns of Genetic Inheritance Lecture Outline Copyright © The McGraw-Hill Companies, Inc."— Presentation transcript:

1 Human Biology Sylvia S. Mader Michael Windelspecht Chapter 20 Patterns of Genetic Inheritance Lecture Outline Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. See separate FlexArt PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes.

2 Points to Ponder What is the genotype and the phenotype of an individual? What are the genotypes for homozygous recessive and dominant individuals and a heterozygote individual? Be able to draw a punnett square for any cross (1-trait cross, 2-trait cross, and a sex-linked cross). What are Tay-Sachs disease, Huntington disease, sickle-cell disease, and PKU? How are each of the above inherited? What is polygenic inheritance? What is a multifactorial trait? What is sex-linked inheritance? Name 3 X-linked recessive disorders. What is codominance? What is incomplete dominance? What do you think about genetic profiling?

3 These traits are genetically inherited Answer these questions about your inheritance: Do you have a widow’s peak? Are your earlobes attached or unattached? Do you have short or long fingers? Do you have freckles? Can you roll your tongue? Do you have Hitchhiker’s thumb? 20.1 Genotype and phenotype

4 Genotype Genotype – specific genes for a particular trait written with symbols –Alleles: alternate forms of a specific gene at the same position (locus) on a gene (e.g., allele for unattached earlobes and attached lobes); alleles occur in pairs –Dominant gene: will be expressed and will mask a recessive gene (Tt or TT) –Recessive allele: allele that is only expressed when a gene has two of this type of allele –Homozygous dominant genotype: 2 dominant alleles (TT or AA) –Homozygous recessive genotype: 2 recessive alleles (tt or aa) –Heterozygous genotype: one dominant allele and one recessive allele (Tt or Aa) 20.1 Genotype and phenotype

5 Phenotype Phenotype – the physical or outward expression of the genotype Genotype Phenotype EE unattached earlobe Ee unattached earlobe ee attached earlobe What are your genotype and phenotype? 20.1 Genotype and phenotype

6 Understanding genotype & phenotype 20.1 Genotype and phenotype Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. sperm egg fertilization growth and development unattached earlobeattached earlobeunattached earlobe Ee eEE ee E eeEE EeeeEE Allele Key E = unattached earlobes e = attached earlobes ee E

7 What about your inheritance? 20.2 One-and Two-trait inheritance

8 Crosses One-trait cross – considers the inheritance of one characteristic e.g. WW x Ww Two-trait cross – considers the inheritance of two characteristics e.g. WWTT x WwTT Gametes only carry one allele, so if an individual has the genotype Ww what are the possible gametes that this individual can pass on? Answer: either a W or a w but not both Another example: 20.2 One-and Two-trait inheritance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. gametes meiosis Offspring × Parents ff ff no freckles ff Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

9 Punnett squares Punnett squares are the use of a grid that diagram crosses between individuals by using the possible parental gametes These allow one to figure the probability that an offspring will have a particular genotype and phenotype 20.2 One-and Two-trait inheritance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3 1 fF F f Key F = Freckles f = No freckles Freckles No freckles Phenotypic Ratio 3:1 Freckles No freckles Offspring Ff ffFf FF × Parents Sperm eggs

10 Practicing punnett squares What would a punnett square involving a man (M) with a genotype Ff and a woman (F) with a genotype Ff look like? F – freckles f – no freckles 20.2 One-and Two-trait inheritance M/F F f FFFFf f ff eggs sperm

11 Practicing ratios Genotypic ratio: the number of offspring with the same genotype Phenotypic ratio: the number of offspring with the same outward appearance What is the genotypic ratio? 1: 2: 1 (1 FF: 2 Ff: 1 ff) What is the phenotypic ratio? 3: 1 (3 with freckles and 1 with no freckles) 20.2 One-and Two-trait inheritance M/F F f FFFFf f ff eggs sperm

12 Monohybrid crosses 20.2 One-and Two-trait inheritance Monohybrid cross – an experimental cross in which parents are identically heterozygous at one gene pair (e.g., Aa x Aa) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ww W W 1 1 × ww W w Offspring Parents wwWW × Parents Wwww Ww ww Offspring ww Ww eggs Straight hairline Widow’s peak Phenotypic Ratio 1:1 Straight hairline Widow’s peak Straight hairline Widow’s peak Key W = w = Widow’s peak Straight hairline Widow’s peak W = w = Key Phenotypic Ratio Widow’s peakAll Ww Sperm a.b.

13 Possible gametes for two traits 20.2 One-and Two-trait inheritance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. SS WW ss ww WW ww WW WWWWwwww WWwwww ss sss ss ss s SS S SSSS SSS WSwswSWs Cell has two pairs of homologues. one pair oreither MEIOSIS I MEIOSIS II Allele Key s = Long fingers S = Short fingers w = Straight hairline W = Widow’s peak

14 Dihybrid cross (a type of two-trait cross) Dihybrid cross – an experimental cross usually involving parents that are homozygous for different alleles of two genes and results in a 9:3:3:1 genotypic ratio for the offspring 20.2 One-and Two-trait inheritance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. P generation P gametes F 1 generation WwSs wwss WWSS ws WS ×

15 Practicing a punnett square for a 2-trait cross What would the punnett square look like for a dihybrid cross between a male that is WWSS and a female that is wwss? 20.2 One-and Two-trait inheritance F 1 gametes F 1 generation wwSs ws wS Ws WS Ws eggs wSws WwSsWwSSWWSsWWSS WwssWwSsWWssWWSs WwSS WwSs Offspring WwsswwSs wwSS sperm Allele Key W = Widow’s peak W = Straight hairline S = Short fingers S = Long fingers Phenotypic Ratio 9:3:3:1 Widow’s peak, short fingers Widow’s peak, long fingers Straight hairline, short fingers Straight hairline, long fingers Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

16 Autosomal recessive disorder Individuals must be homozygous recessive to have the disorder 20.3 Inheritance of genetic disorders Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. II III IV I aa A? Aa A?aa Aa * relatives Aa Key = affected Aa = carrier (unaffected) AA = unaffected A? = unaffected (one allele unknown) aa AaA? Autosomal recessive disorders Affected children can have unaffected parents. Heterozygotes (Aa) have an unaffected phenotype. Two affected parents will always have affected children. Affected individuals with homozygous unaffected mates will have unaffected children. Close relatives who reproduce are more likely to have affected children. Both males and females are affected with equal frequency.

17 Autosomal dominant disorder Individuals that are homozygous dominant and heterozygous will have the disorder 20.3 Inheritance of genetic disorders Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. aa = unaffected (one allele unknown) = affected AA Aa A? 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. III II I Aa aa Aa * A?aa Aa Key

18 Genetic disorders of interest Tay-Sachs disease: lack of the enzyme that breaks down lipids in lysosomes resulting in excess and eventually death of a baby Cystic fibrosis: Cl - do not pass normally through a cell membrane resulting in thick mucus in lungs and other places often causing infections Phenylketonuria (PKU): lack of an enzyme needed to make a certain amino acid and affects nervous system development Sickle-Cell disease: red-blood cells are sickle shaped rather than biconcave that clog blood vessels Huntington disease: huntington protein has too many glutamine amino acids leading to the progressive degeneration of brain cells 20.3 Inheritance of genetic disorders

19 Genetic disorders 20.3 Inheritance of genetic disorders Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. many neurons in normal brain loss of neurons in huntington brain Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (both brain tissue slides): Courtesy Dr. Hemachandra Reddy, The Neurological Science Institute, Oregon Health & Science University; (woman with Huntington): © Steve Uzzell Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. thick mucus defective channel H2OH2O H2OH2O Cl – H2OH2O Cl nebulizer percussion vest © Pat Pendarvis

20 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

21 Polygenic inheritance Polygenic traits - two or more sets of alleles govern one trait –Each dominant allele codes for a product so these effects are additive –Results in a continuous variation of phenotypes –Environmental effects cause intervening phenotypes –e.g., skin color ranges from very dark to very light –e.g., height varies among Multifactorial trait – a polygenic trait that is particularly influenced by the environment –e.g., skin color is influenced by sun exposure –e.g., height can be affected by nutrition 20.4 Beyond simple inheritance patterns

22 Polygenic inheritance 20.4 Beyond simple inheritance patterns Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. most are this height Height in Inches tallshort few Number of Men Courtesy University of Connecticut/Peter Morenus, photographer 62 Dark aabb AABB GenotypesPhenotypes AABb or AaBB AaBb or Aabb or aaBB Aabb or aaBb Very dark Medium brown Light Very light Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

23 Demonstrating environmental influences on phenotype Himalayan rabbit’s coat color influenced by temperature There is an allele responsible for melanin production that appears to be active only at lower temperatures The extremities have a lower temperature and thus the ears, nose, paws, and tail are dark in color 20.4 Beyond simple inheritance patterns

24 Incomplete dominance Occurs when the heterozygote is intermediate between the 2 homozygotes Example: (curly hair) CC x SS (straight hair) CS (wavy hair) 20.4 Beyond simple inheritance patterns

25 Codominance Occurs when the alleles are equally expressed in a heterozygote Example: (Type A blood) AA x BB (Type B blood) AB (Type AB blood that has characteristics of both blood types) 20.4 Beyond simple inheritance patterns

26 Multiple allele inheritance The gene exists in several allelic forms A person only has 2 of the possible alleles A good example is the ABO blood system A and B are codominant alleles The O alleles is recessive to both A and B therefore to have this blood type you must have 2 recessive alleles 20.4 Beyond simple inheritance patterns

27 Multiple allele inheritance Based on what you know what type of blood would each of the following individuals have in a cross between Ao and Bo? possible genotypes:phenotypes: ABType AB blood BoType B blood AoType A blood ooType O blood 20.4 Beyond simple inheritance patterns

28 Blood type inheritance 20.4 Beyond simple inheritance patterns Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. × Parents eggs Phenotypic Ratio 1:1:1:1 Blood type A Blood type B Blood type AB Blood type O Key ii i i IBiIBiIAiIAi IBiIBiIBIB IBIB IAIBIAIB IAiIAi sperm Offspring

29 Sex-linked inheritance Traits are controlled by genes on the sex chromosomes  X-linked inheritance: the allele is carried on the X chromosome  Y-linked inheritance: the allele is carried on the Y chromosome  Most sex-linked traits are X-linked 20.5 Sex-linked inheritance

30 X-linked inheritance: Color blindness Cross: X B X b x X B Y Possible offspring: X B X B normal vision female X B X b normal vision female X B Y normal vision male X b Y normal vision male 20.5 Sex-linked inheritance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. × Parents Key X B = Normal vision X b = Color-blind Normal vision Color-blind Phenotypic Ratio Females All Males 1:1 1 1 XbYXbYXBYXBY XBXbXBXb XBXBXBXB XbXb XBXB XBXB Y eggs XBYXBYXBXbXBXb Offspring sperm

31 X-linked disorders More often found in males than females because recessive alleles are always expressed Most X-linked disorders are recessive: –Color blindness: most often characterized by red- green color blindness –Muscular dystrophy: characterized by wasting of muscles and death by age 20 –Fragile X syndrome: most common cause of inherited mental impairment –Hemophilia: characterized by the absence of particular clotting factors that causes blood to clot very slowly or not at all 20.5 Sex-linked inheritance

32 X-linked disorders 20.5 Sex-linked inheritance 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. grandson daughter grandfather XBXBXBXB XBYXBYXBXbXBXb XBYXBYXbXbXbXb XbYXbY XbYXbYXBYXBYXBXBXBXB XBXbXBXb XbYXbY Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

33 X-linked disorders: Hemophilia 20.5 Sex-linked inheritance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Unaffected male Hemophiliac male Unaffected female Carrier female ?? ?? ?? Nicholas IIAlexandra Olga All were assassinated Anastasia Philip Harry Juan Carlos Elizabeth II MarieAlexi Mary Alice1210Louis IV 2. Edward VII 3. Irene 4. George V 6. Margaret 9. Juan 12. Diana 14. Edward 16. Sarah LeopoldBeatriceHelena Albert Edward ??? ? 1. Victoria 7. Victoria 8. Alfonso XIII Tatiana Victoria Alexandra 11. Charles 13. Andrew 15. Anne Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (queen): © Stapleton Collection/ Corbis; (prince): © Huton Archive/Getty Images William


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