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Human Biology Sylvia S. Mader Michael Windelspecht
Chapter 20 Patterns of Genetic Inheritance Lecture Outline See separate FlexArt PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1
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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?
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These traits are genetically inherited
20.1 Genotype and phenotype 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?
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20.1 Genotype and phenotype
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)
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20.1 Genotype and 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?
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Understanding genotype & phenotype
20.1 Genotype and phenotype Understanding genotype & phenotype Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. egg E e E E E e e e e sperm fertilization EE ee Ee growth and development EE ee Ee unattached earlobe attached earlobe unattached earlobe Allele Key E = unattached earlobes e = attached earlobes
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What about your inheritance?
20.2 One-and Two-trait inheritance What about your inheritance?
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Crosses × 20.2 One-and Two-trait inheritance Parents no freckles
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: Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Parents no freckles no freckles × ff ff meiosis gametes f f Offspring ff no freckles
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20.2 One-and Two-trait inheritance
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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Parents Ff × Ff Key F = Freckles eggs f = No freckles Freckles F f No freckles F FF Ff Phenotypic Ratio 3:1 Sperm 3 Freckles f Ff ff 1 No freckles Offspring
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Practicing punnett squares
20.2 One-and Two-trait inheritance Practicing punnett squares eggs 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 M/F F f FF Ff ff sperm
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Practicing ratios F f FF Ff ff M/F
20.2 One-and Two-trait inheritance 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) eggs M/F F f FF Ff ff sperm
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20.2 One-and Two-trait inheritance
Monohybrid crosses 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. Parents Parents WW × ww Ww × ww Key W = Widow’s peak Key eggs eggs w = Straight hairline W = Widow’s peak Widow’s peak w w w = Straight hairline w w Straight hairline Widow’s peak Straight hairline W Ww Ww W Ww Ww Phenotypic Ratio 1:1 Sperm Sperm Phenotypic Ratio 1 Widow’s peak W Ww Ww All Widow’s peak w ww ww 1 Straight hairline Offspring Offspring a. b.
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Possible gametes for two traits
20.2 One-and Two-trait inheritance Possible gametes for two traits Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. one pair Allele Key Cell has two pairs of homologues. W = Widow’s peak w = Straight hairline one pair S = Short fingers s = Long fingers either or MEIOSIS I S S s s S S s s W W W W w w w w MEIOSIS II S S s s S S s s W W w w w w W W S S s s S S s s W W w w w w W W WS ws wS Ws
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Dihybrid cross (a type of two-trait cross)
20.2 One-and Two-trait inheritance 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. × P generation WWSS wwss P gametes WS ws F1generation WwSs
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Practicing a punnett square for a 2-trait cross
20.2 One-and Two-trait inheritance 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? Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. eggs F1gametes WS Ws wS ws WS WWSS WWSs WwSS WwSs F1generation Ws sperm WWSs WWss WwSs Wwss wS WwSS wwSS wwSs ws WwSs Wwss wwSs Offspring Allele Key W = Widow’s peak W = Straight hairline S = Short fingers S = Long fingers Phenotypic Ratio 9:3:3:1 9 Widow’s peak, short fingers 3 Widow’s peak, long fingers 3 Straight hairline, short fingers 1 Straight hairline, long fingers
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Autosomal recessive disorder
20.3 Inheritance of genetic disorders Autosomal recessive disorder Individuals must be homozygous recessive to have the disorder Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. I aa A? II A? Aa Aa A? * relatives III Aa Aa A? A? IV aa aa A? Key aa = affected Aa = carrier (unaffected) AA = unaffected Autosomal recessive disorders A? = unaffected Affected children can have unaffected parents. (one allele unknown) 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.
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Autosomal dominant disorder
20.3 Inheritance of genetic disorders Autosomal dominant disorder Individuals that are homozygous dominant and heterozygous will have the disorder Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. I Aa Aa * II aa Aa A? aa aa aa III Aa Aa aa aa aa aa Key AA = affected Aa = affected Autosomal dominant disorders A? = affected • Affected children will usually have an affected parent. (one allele unknown) aa = unaffected • 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.
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Genetic disorders of interest
20.3 Inheritance of genetic disorders 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
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Genetic disorders 20.3 Inheritance of genetic disorders Cl– nebulizer
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cl– nebulizer percussion vest H2O Cl– Cl– H2O Cl Cl H2O many neurons in normal brain defective channel thick mucus loss of neurons in huntington brain (both brain tissue slides): Courtesy Dr. Hemachandra Reddy, The Neurological Science Institute, Oregon Health & Science University; (woman with Huntington): © Steve Uzzell © Pat Pendarvis
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Polygenic inheritance
20.4 Beyond simple inheritance patterns 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
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Polygenic inheritance
20.4 Beyond simple inheritance patterns Polygenic inheritance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Genotypes Phenotypes AABB Very dark AABb or AaBB Dark AaBb or Aabb or aaBB Medium brown Aabb or aaBb Light aabb Very light Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. most are this height Number of Men few few 62 64 66 68 70 72 74 short tall Height in Inches Courtesy University of Connecticut/Peter Morenus, photographer
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Demonstrating environmental influences on phenotype
20.4 Beyond simple inheritance patterns 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
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20.4 Beyond simple inheritance patterns
Incomplete dominance Occurs when the heterozygote is intermediate between the 2 homozygotes Example: (curly hair) CC x SS (straight hair) CS (wavy hair)
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20.4 Beyond simple inheritance patterns
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)
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Multiple allele inheritance
20.4 Beyond simple inheritance patterns 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
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Multiple allele inheritance
20.4 Beyond simple inheritance patterns 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: AB Type AB blood Bo Type B blood Ao Type A blood oo Type O blood
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Blood type inheritance
20.4 Beyond simple inheritance patterns Blood type inheritance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Parents × Key IBi IAi Blood type A Blood type B Blood type AB eggs Blood type O IB i Phenotypic Ratio 1:1:1:1 IB IAIB IBi 1 sperm 1 1 i IAi ii 1 Offspring
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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
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X-linked inheritance: Color blindness
20.5 Sex-linked inheritance X-linked inheritance: Color blindness Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cross: XBXb x XBY Possible offspring: XBXB normal vision female XBXb normal vision female XBY normal vision male XbY normal vision male Parents × Key XBY XBXb XB = Normal vision Xb = Color-blind Normal vision eggs Color-blind XB Xb Phenotypic Ratio XB XBXB XBXb Females All sperm Males 1:1 1 Y XBY XbY 1 Offspring
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20.5 Sex-linked inheritance
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
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X-linked disorders 20.5 Sex-linked inheritance XBXB XbY grandfather
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. XBXB XbY grandfather XBY XBXb daughter XBY XbXb XbY XBY XBXB XBXb XbY grandson Key XBXB = Unaffected female XBXb = Carrier female XbXb = Color-blind female XBY = Unaffected male X-linked Recessive Disorders XbY = 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.
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X-linked disorders: Hemophilia
20.5 Sex-linked inheritance X-linked disorders: Hemophilia Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Unaffected female Unaffected male Victoria Edward Carrier female Hemophiliac male Victoria Albert 1 Alice Louis IV 2 10 Leopold Beatrice Helena 3 Alexandra Nicholas II 4 Mary 7 8 ? ? ? ? ? ? ? Olga Marie Alexi 9 Tatiana Anastasia ? ? ? Juan Carlos 5 All were assassinated 6 1. Victoria 10. Alexandra 2. Edward VII Philip Elizabeth II 11. Charles 3. Irene 12. Diana 4. George V 13. Andrew 6. Margaret 14. Edward 7. Victoria 12 11 13 16 14 15 15. Anne 8. Alfonso XIII 16. Sarah 9. Juan William Harry (queen): © Stapleton Collection/ Corbis; (prince): © Huton Archive/Getty Images
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