Chapter 14 mendel

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Chapter 14 mendel

  1. 1. LECTURE PRESENTATIONSFor CAMPBELL BIOLOGY, NINTH EDITIONJane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson© 2011 Pearson Education, Inc.Lectures byErin BarleyKathleen FitzpatrickMendel and the Gene IdeaChapter 14
  2. 2. Overview: Drawing from the Deck of Genes• What genetic principles account for the passingof traits from parents to offspring?• The “blending” hypothesis is the idea thatgenetic material from the two parents blendstogether (like blue and yellow paint blend tomake green)© 2011 Pearson Education, Inc.
  3. 3. • The “particulate” hypothesis is the idea thatparents pass on discrete heritable units(genes)• This hypothesis can explain the reappearanceof traits after several generations• Mendel documented a particulate mechanismthrough his experiments with garden peas© 2011 Pearson Education, Inc.
  4. 4. Figure 14.1
  5. 5. Concept 14.1: Mendel used the scientificapproach to identify two laws of inheritance• Mendel discovered the basic principles ofheredity by breeding garden peas in carefullyplanned experiments© 2011 Pearson Education, Inc.
  6. 6. Mendel’s Experimental, QuantitativeApproach• Advantages of pea plants for genetic study– There are many varieties with distinct heritablefeatures, or characters (such as flower color);character variants (such as purple or whiteflowers) are called traits– Mating can be controlled– Each flower has sperm-producing organs(stamens) and egg-producing organ (carpel)– Cross-pollination (fertilization between differentplants) involves dusting one plant with pollenfrom another© 2011 Pearson Education, Inc.
  7. 7. Figure 14.2Parentalgeneration(P)StamensCarpelFirst filialgenerationoffspring(F1)TECHNIQUERESULTS32145
  8. 8. Figure 14.2aParentalgeneration(P) StamensCarpelTECHNIQUE2134
  9. 9. Figure 14.2bFirst filialgenerationoffspring(F1)RESULTS5
  10. 10. • Mendel chose to track only those charactersthat occurred in two distinct alternative forms• He also used varieties that were true-breeding(plants that produce offspring of the samevariety when they self-pollinate)© 2011 Pearson Education, Inc.
  11. 11. • In a typical experiment, Mendel mated twocontrasting, true-breeding varieties, a processcalled hybridization• The true-breeding parents are the P generation• The hybrid offspring of the P generation are calledthe F1 generation• When F1 individuals self-pollinate or cross-pollinate with other F1 hybrids, the F2 generation isproduced© 2011 Pearson Education, Inc.
  12. 12. The Law of Segregation• When Mendel crossed contrasting, true-breeding white- and purple-flowered pea plants,all of the F1 hybrids were purple• When Mendel crossed the F1 hybrids, many ofthe F2 plants had purple flowers, but some hadwhite• Mendel discovered a ratio of about three to one,purple to white flowers, in the F2 generation© 2011 Pearson Education, Inc.
  13. 13. Figure 14.3-1P GenerationEXPERIMENT(true-breedingparents) PurpleflowersWhiteflowers
  14. 14. Figure 14.3-2P GenerationEXPERIMENT(true-breedingparents)F1 Generation(hybrids)PurpleflowersWhiteflowersAll plants had purple flowersSelf- or cross-pollination
  15. 15. Figure 14.3-3P GenerationEXPERIMENT(true-breedingparents)F1 Generation(hybrids)F2 GenerationPurpleflowersWhiteflowersAll plants had purple flowersSelf- or cross-pollination705 purple-floweredplants224 whitefloweredplants
  16. 16. • Mendel reasoned that only the purple flowerfactor was affecting flower color in the F1 hybrids• Mendel called the purple flower color a dominanttrait and the white flower color a recessive trait• The factor for white flowers was not diluted ordestroyed because it reappeared in the F2generation© 2011 Pearson Education, Inc.
  17. 17. • Mendel observed the same pattern ofinheritance in six other pea plant characters,each represented by two traits• What Mendel called a “heritable factor” is whatwe now call a gene© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.
  18. 18. Table 14.1
  19. 19. Mendel’s Model• Mendel developed a hypothesis to explain the3:1 inheritance pattern he observed in F2offspring• Four related concepts make up this model• These concepts can be related to what we nowknow about genes and chromosomes© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.
  20. 20. • First: alternative versions of genes account forvariations in inherited characters• For example, the gene for flower color in peaplants exists in two versions, one for purpleflowers and the other for white flowers• These alternative versions of a gene are nowcalled alleles• Each gene resides at a specific locus on aspecific chromosome© 2011 Pearson Education, Inc.
  21. 21. Figure 14.4Allele for purple flowersLocus for flower-color geneAllele for white flowersPair ofhomologouschromosomes
  22. 22. • Second: for each character, an organisminherits two alleles, one from each parent• Mendel made this deduction without knowingabout the role of chromosomes• The two alleles at a particular locus may beidentical, as in the true-breeding plants ofMendel’s P generation• Alternatively, the two alleles at a locus maydiffer, as in the F1 hybrids© 2011 Pearson Education, Inc.
  23. 23. • Third: if the two alleles at a locus differ, then one(the dominant allele) determines the organism’sappearance, and the other (the recessive allele)has no noticeable effect on appearance• In the flower-color example, the F1 plants hadpurple flowers because the allele for that trait isdominant© 2011 Pearson Education, Inc.
  24. 24. • Fourth: (now known as the law of segregation):the two alleles for a heritable character separate(segregate) during gamete formation and end upin different gametes• Thus, an egg or a sperm gets only one of the twoalleles that are present in the organism• This segregation of alleles corresponds to thedistribution of homologous chromosomes todifferent gametes in meiosis© 2011 Pearson Education, Inc.
  25. 25. • Mendel’s segregation model accounts for the 3:1ratio he observed in the F2 generation of hisnumerous crosses• The possible combinations of sperm and egg canbe shown using a Punnett square, a diagram forpredicting the results of a genetic cross betweenindividuals of known genetic makeup• A capital letter represents a dominant allele, and alowercase letter represents a recessive allele© 2011 Pearson Education, Inc.
  26. 26. Figure 14.5-1P GenerationAppearance:Genetic makeup:Gametes:Purple flowers White flowersPP ppP p
  27. 27. Figure 14.5-2P GenerationF1 GenerationAppearance:Genetic makeup:Gametes:Appearance:Genetic makeup:Gametes:Purple flowers White flowersPurple flowersPpPP ppPPpp1/21/2
  28. 28. Figure 14.5-3P GenerationF1 GenerationF2 GenerationAppearance:Genetic makeup:Gametes:Appearance:Genetic makeup:Gametes:Purple flowers White flowersPurple flowersSperm from F1 (Pp) plantPpPP ppPPPPppppEggs fromF1 (Pp) plantPPppPpPp1/21/23 : 1
  29. 29. Useful Genetic Vocabulary• An organism with two identical alleles for acharacter is said to be homozygous for thegene controlling that character• An organism that has two different alleles for agene is said to be heterozygous for the genecontrolling that character• Unlike homozygotes, heterozygotes are nottrue-breeding© 2011 Pearson Education, Inc.
  30. 30. • Because of the different effects of dominant andrecessive alleles, an organism’s traits do notalways reveal its genetic composition• Therefore, we distinguish between an organism’sphenotype, or physical appearance, and itsgenotype, or genetic makeup• In the example of flower color in pea plants, PPand Pp plants have the same phenotype (purple)but different genotypes© 2011 Pearson Education, Inc.
  31. 31. PhenotypePurplePurplePurpleWhite31112Ratio 3:1 Ratio 1:2:1GenotypePP(homozygous)Pp(heterozygous)Pp(heterozygous)pp(homozygous)Figure 14.6
  32. 32. The Testcross• How can we tell the genotype of an individual withthe dominant phenotype?• Such an individual could be either homozygousdominant or heterozygous• The answer is to carry out a testcross: breedingthe mystery individual with a homozygousrecessive individual• If any offspring display the recessive phenotype,the mystery parent must be heterozygous© 2011 Pearson Education, Inc.
  33. 33. Figure 14.7Dominant phenotype,unknown genotype:PP or Pp?Recessive phenotype,known genotype:ppPredictionsIf purple-floweredparent is PPIf purple-floweredparent is PporSperm SpermEggs EggsorAll offspring purple 1/2 offspring purple and1/2 offspring whitePp PpPp PpPp Pppp ppp p p pPPPpTECHNIQUERESULTS
  34. 34. The Law of Independent Assortment• Mendel derived the law of segregation byfollowing a single character• The F1 offspring produced in this cross weremonohybrids, individuals that areheterozygous for one character• A cross between such heterozygotes is calleda monohybrid cross© 2011 Pearson Education, Inc.
  35. 35. • Mendel identified his second law of inheritance byfollowing two characters at the same time• Crossing two true-breeding parents differing in twocharacters produces dihybrids in the F1generation, heterozygous for both characters• A dihybrid cross, a cross between F1 dihybrids,can determine whether two characters aretransmitted to offspring as a package orindependently© 2011 Pearson Education, Inc.
  36. 36. Figure 14.8P GenerationF1 GenerationPredictionsGametesEXPERIMENTRESULTSYYRR yyrryrYRYyRrHypothesis ofdependent assortmentHypothesis ofindependent assortmentPredictedoffspring ofF2 generationSpermSpermorEggsEggsPhenotypic ratio 3:1Phenotypic ratio 9:3:3:1Phenotypic ratio approximately 9:3:3:1315 108 101 321/21/21/21/21/41/41/41/41/41/41/41/49/163/163/161/16YRYRYRYRyryryryr1/43/4YrYryRyRYYRR YyRrYyRr yyrrYYRR YYRr YyRR YyRrYYRr YYrr YyRr YyrrYyRR YyRr yyRR yyRrYyRr Yyrr yyRr yyrr
  37. 37. • Using a dihybrid cross, Mendel developed thelaw of independent assortment• The law of independent assortment states thateach pair of alleles segregates independently ofeach other pair of alleles during gameteformation• Strictly speaking, this law applies only to geneson different, nonhomologous chromosomes orthose far apart on the same chromosome• Genes located near each other on the samechromosome tend to be inherited together© 2011 Pearson Education, Inc.
  38. 38. Concept 14.2: The laws of probability governMendelian inheritance• Mendel’s laws of segregation and independentassortment reflect the rules of probability• When tossing a coin, the outcome of one tosshas no impact on the outcome of the next toss• In the same way, the alleles of one genesegregate into gametes independently ofanother gene’s alleles© 2011 Pearson Education, Inc.
  39. 39. • The multiplication rule states that the probabilitythat two or more independent events will occurtogether is the product of their individualprobabilities• Probability in an F1 monohybrid cross can bedetermined using the multiplication rule• Segregation in a heterozygous plant is like flippinga coin: Each gamete has a chance of carryingthe dominant allele and a chance of carrying therecessive alleleThe Multiplication and Addition RulesApplied to Monohybrid Crosses1212© 2011 Pearson Education, Inc.
  40. 40. Figure 14.9Segregation ofalleles into eggsSegregation ofalleles into spermSpermEggs1/21/21/21/21/41/41/41/4Rr RrRRRRRRrrrr r×r
  41. 41. • The addition rule states that the probability thatany one of two or more exclusive events willoccur is calculated by adding together theirindividual probabilities• The rule of addition can be used to figure out theprobability that an F2 plant from a monohybridcross will be heterozygous rather thanhomozygous© 2011 Pearson Education, Inc.
  42. 42. Solving Complex Genetics Problems with theRules of Probability• We can apply the multiplication and additionrules to predict the outcome of crosses involvingmultiple characters• A dihybrid or other multicharacter cross isequivalent to two or more independentmonohybrid crosses occurring simultaneously• In calculating the chances for various genotypes,each character is considered separately, andthen the individual probabilities are multiplied© 2011 Pearson Education, Inc.
  43. 43. Figure 14.UN01Probability of YYRRProbability of YyRR1/4 (probability of YY)1/2 (Yy)1/4 (RR)1/4 (RR)1/161/8= ××===
  44. 44. Figure 14.UN02Chance of at least two recessive traitsppyyRrppYyrrPpyyrrPPyyrrppyyrr1/4 (probability of pp) × 1/2 (yy) × 1/2 (Rr)1/4 × 1/2 × 1/21/2 × 1/2 × 1/21/4 × 1/2 × 1/21/4 × 1/2 × 1/2= 1/16= 1/16= 2/16= 1/16= 1/16= 6/16 or 3/8
  45. 45. Concept 14.3: Inheritance patterns are oftenmore complex than predicted by simpleMendelian genetics• The relationship between genotype andphenotype is rarely as simple as in the peaplant characters Mendel studied• Many heritable characters are not determinedby only one gene with two alleles• However, the basic principles of segregationand independent assortment apply even tomore complex patterns of inheritance© 2011 Pearson Education, Inc.
  46. 46. Extending Mendelian Genetics for a SingleGene• Inheritance of characters by a single gene maydeviate from simple Mendelian patterns in thefollowing situations:– When alleles are not completely dominant orrecessive– When a gene has more than two alleles– When a gene produces multiple phenotypes© 2011 Pearson Education, Inc.
  47. 47. Degrees of Dominance• Complete dominance occurs when phenotypesof the heterozygote and dominant homozygote areidentical• In incomplete dominance, the phenotype of F1hybrids is somewhere between the phenotypes ofthe two parental varieties• In codominance, two dominant alleles affect thephenotype in separate, distinguishable ways© 2011 Pearson Education, Inc.
  48. 48. Figure 14.10-1P GenerationRed WhiteGametesCWCWCRCRCR CW
  49. 49. Figure 14.10-2P GenerationF1 Generation1/21/2Red WhiteGametesPinkGametesCWCWCRCRCR CWCRCWCRCW
  50. 50. Figure 14.10-3P GenerationF1 GenerationF2 Generation1/21/21/21/21/21/2Red WhiteGametesPinkGametesSpermEggsCWCWCRCRCRCWCRCWCRCWCWCRCRCWCRCRCRCWCRCWCWCW
  51. 51. • A dominant allele does not subdue a recessiveallele; alleles don’t interact that way• Alleles are simply variations in a gene’snucleotide sequence• For any character, dominance/recessivenessrelationships of alleles depend on the level atwhich we examine the phenotypeThe Relation Between Dominance andPhenotype© 2011 Pearson Education, Inc.
  52. 52. • Tay-Sachs disease is fatal; a dysfunctionalenzyme causes an accumulation of lipids in thebrain– At the organismal level, the allele is recessive– At the biochemical level, the phenotype (i.e.,the enzyme activity level) is incompletelydominant– At the molecular level, the alleles arecodominant© 2011 Pearson Education, Inc.
  53. 53. Frequency of Dominant Alleles• Dominant alleles are not necessarily morecommon in populations than recessive alleles• For example, one baby out of 400 in the UnitedStates is born with extra fingers or toes© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.
  54. 54. • The allele for this unusual trait is dominant to theallele for the more common trait of five digits perappendage• In this example, the recessive allele is far moreprevalent than the population’s dominant allele© 2011 Pearson Education, Inc.
  55. 55. Multiple Alleles• Most genes exist in populations in more than twoallelic forms• For example, the four phenotypes of the ABOblood group in humans are determined by threealleles for the enzyme (I) that attaches A or Bcarbohydrates to red blood cells: IA, IB, and i.• The enzyme encoded by the IAallele adds the Acarbohydrate, whereas the enzyme encoded bythe IBallele adds the B carbohydrate; the enzymeencoded by the i allele adds neither© 2011 Pearson Education, Inc.
  56. 56. Figure 14.11CarbohydrateAllele(a) The three alleles for the ABO blood groups and theircarbohydrates(b) Blood group genotypes and phenotypesGenotypeRed blood cellappearancePhenotype(blood group)AABB ABnoneOIAIBiiiIAIBIAIAor IAi IBIBor IBi
  57. 57. Pleiotropy• Most genes have multiple phenotypic effects, aproperty called pleiotropy• For example, pleiotropic alleles are responsible forthe multiple symptoms of certain hereditarydiseases, such as cystic fibrosis and sickle-celldisease© 2011 Pearson Education, Inc.
  58. 58. Extending Mendelian Genetics for Two orMore Genes• Some traits may be determined by two or moregenes© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.
  59. 59. Epistasis• In epistasis, a gene at one locus alters thephenotypic expression of a gene at a secondlocus• For example, in Labrador retrievers and manyother mammals, coat color depends on twogenes• One gene determines the pigment color (withalleles B for black and b for brown)• The other gene (with alleles C for color and cfor no color) determines whether the pigmentwill be deposited in the hair© 2011 Pearson Education, Inc.
  60. 60. Figure 14.12SpermEggs9 : 3 : 41/41/41/41/41/41/41/41/4BbEe BbEeBEBEbEbEBeBebebeBBEE BbEE BBEe BbEeBbEE bbEE BbEe bbEeBBEe BbEe BBee BbeeBbEe bbEe Bbee bbee
  61. 61. Polygenic Inheritance• Quantitative characters are those that vary in thepopulation along a continuum• Quantitative variation usually indicates polygenicinheritance, an additive effect of two or moregenes on a single phenotype• Skin color in humans is an example of polygenicinheritance© 2011 Pearson Education, Inc.
  62. 62. Figure 14.13EggsSpermPhenotypes:Number ofdark-skin alleles: 0 1 2 3 4 5 61/81/81/81/81/81/81/81/81/81/81/81/81/81/81/81/81/646/6415/6420/6415/646/641/64AaBbCc AaBbCc
  63. 63. Nature and Nurture: The EnvironmentalImpact on Phenotype• Another departure from Mendelian geneticsarises when the phenotype for a characterdepends on environment as well as genotype• The norm of reaction is the phenotypic rangeof a genotype influenced by the environment• For example, hydrangea flowers of the samegenotype range from blue-violet to pink,depending on soil acidity© 2011 Pearson Education, Inc.
  64. 64. Figure 14.14
  65. 65. Figure 14.14a
  66. 66. Figure 14.14b
  67. 67. • Norms of reaction are generally broadest forpolygenic characters• Such characters are called multifactorialbecause genetic and environmental factorscollectively influence phenotype© 2011 Pearson Education, Inc.
  68. 68. Integrating a Mendelian View of Heredityand Variation• An organism’s phenotype includes its physicalappearance, internal anatomy, physiology, andbehavior• An organism’s phenotype reflects its overallgenotype and unique environmental history© 2011 Pearson Education, Inc.
  69. 69. Concept 14.4: Many human traits followMendelian patterns of inheritance• Humans are not good subjects for geneticresearch– Generation time is too long– Parents produce relatively few offspring– Breeding experiments are unacceptable• However, basic Mendelian genetics enduresas the foundation of human genetics© 2011 Pearson Education, Inc.
  70. 70. Pedigree Analysis• A pedigree is a family tree that describes theinterrelationships of parents and childrenacross generations• Inheritance patterns of particular traits can betraced and described using pedigrees© 2011 Pearson Education, Inc.
  71. 71. Figure 14.15KeyMale Female AffectedmaleAffectedfemaleMating Offspring1stgeneration2ndgeneration3rdgeneration1stgeneration2ndgeneration3rdgenerationIs a widow’s peak a dominant orrecessive trait?(a) Is an attached earlobe a dominantor recessive trait?b)Widow’speakNo widow’speakAttachedearlobeFreeearlobeFForFfWWorWwWw ww ww WwWw Ww Wwww ww wwwwFf Ff FfFf FfffffffffFF or Ffff
  72. 72. Figure 14.15aWidow’speak
  73. 73. Figure 14.15bNo widow’speak
  74. 74. Figure 14.15cAttachedearlobe
  75. 75. Figure 14.15dFreeearlobe
  76. 76. • Pedigrees can also be used to makepredictions about future offspring• We can use the multiplication and additionrules to predict the probability of specificphenotypes© 2011 Pearson Education, Inc.
  77. 77. Recessively Inherited Disorders• Many genetic disorders are inherited in arecessive manner• These range from relatively mild to life-threatening© 2011 Pearson Education, Inc.
  78. 78. The Behavior of Recessive Alleles• Recessively inherited disorders show up only inindividuals homozygous for the allele• Carriers are heterozygous individuals whocarry the recessive allele but are phenotypicallynormal; most individuals with recessivedisorders are born to carrier parents• Albinism is a recessive condition characterizedby a lack of pigmentation in skin and hair© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.
  79. 79. Figure 14.16ParentsNormalAaSpermEggsNormalAaAANormalAaNormal(carrier)AaNormal(carrier)aaAlbinoAAaa
  80. 80. Figure 14.16a
  81. 81. • If a recessive allele that causes a disease israre, then the chance of two carriers meetingand mating is low• Consanguineous matings (i.e., matingsbetween close relatives) increase the chanceof mating between two carriers of the samerare allele• Most societies and cultures have laws ortaboos against marriages between closerelatives© 2011 Pearson Education, Inc.
  82. 82. Cystic Fibrosis• Cystic fibrosis is the most common lethalgenetic disease in the United States,strikingone out of every 2,500 people of Europeandescent• The cystic fibrosis allele results in defective orabsent chloride transport channels in plasmamembranes leading to a buildup of chlorideions outside the cell• Symptoms include mucus buildup in someinternal organs and abnormal absorption ofnutrients in the small intestine© 2011 Pearson Education, Inc.
  83. 83. Sickle-Cell Disease: A Genetic Disorder withEvolutionary Implications• Sickle-cell disease affects one out of 400African-Americans• The disease is caused by the substitution of asingle amino acid in the hemoglobin protein inred blood cells• In homozygous individuals, all hemoglobin isabnormal (sickle-cell)• Symptoms include physical weakness, pain,organ damage, and even paralysis© 2011 Pearson Education, Inc.
  84. 84. Fig. 14-UN1© 2011 Pearson Education, Inc.• Heterozygotes (said to have sickle-cell trait) areusually healthy but may suffer some symptoms• About one out of ten African Americans hassickle cell trait, an unusually high frequency ofan allele with detrimental effects inhomozygotes• Heterozygotes are less susceptible to themalaria parasite, so there is an advantage tobeing heterozygous
  85. 85. Dominantly Inherited Disorders• Some human disorders are caused bydominant alleles• Dominant alleles that cause a lethal diseaseare rare and arise by mutation• Achondroplasia is a form of dwarfism causedby a rare dominant allele© 2011 Pearson Education, Inc.
  86. 86. Figure 14.17ParentsDwarfDdSpermEggsDdDwarfddNormalDdDwarfddNormalDdddNormaldd
  87. 87. Figure 14.17a
  88. 88. • The timing of onset of a disease significantlyaffects its inheritance• Huntington’s disease is a degenerative diseaseof the nervous system• The disease has no obvious phenotypic effectsuntil the individual is about 35 to 40 years of age• Once the deterioration of the nervous systembegins the condition is irreversible and fatalHuntington’s Disease: A Late-Onset LethalDisease© 2011 Pearson Education, Inc.
  89. 89. Multifactorial Disorders• Many diseases, such as heart disease,diabetes, alcoholism, mental illnesses, andcancer have both genetic and environmentalcomponents• Little is understood about the geneticcontribution to most multifactorial diseases© 2011 Pearson Education, Inc.
  90. 90. Genetic Testing and Counseling• Genetic counselors can provide information toprospective parents concerned about a familyhistory for a specific disease© 2011 Pearson Education, Inc.
  91. 91. Counseling Based on Mendelian Geneticsand Probability Rules• Using family histories, genetic counselors helpcouples determine the odds that their childrenwill have genetic disorders• Probabilities are predicted on the mostaccurate information at the time; predictedprobabilities may change as new informationis available© 2011 Pearson Education, Inc.
  92. 92. Tests for Identifying Carriers• For a growing number of diseases, tests areavailable that identify carriers and help define theodds more accurately© 2011 Pearson Education, Inc.
  93. 93. Figure 14.18
  94. 94. Fetal Testing• In amniocentesis, the liquid that bathes thefetus is removed and tested• In chorionic villus sampling (CVS), a sampleof the placenta is removed and tested• Other techniques, such as ultrasound andfetoscopy, allow fetal health to be assessedvisually in utero© 2011 Pearson Education, Inc.Video: Ultrasound of Human Fetus I
  95. 95. Figure 14.19(a) Amniocentesis (b) Chorionic villus sampling (CVS)Ultrasound monitorAmnioticfluidwithdrawnFetusPlacentaUterus CervixCentrifugationFluidFetalcellsSeveral hoursSeveralweeksSeveral weeksBiochemicaland genetictestsKaryotypingUltrasoundmonitorFetusPlacentaChorionic villiUterusCervixSuctiontubeinsertedthroughcervixSeveralhoursFetal cellsSeveral hours11223
  96. 96. Newborn Screening• Some genetic disorders can be detected at birthby simple tests that are now routinely performedin most hospitals in the United States© 2011 Pearson Education, Inc.
  97. 97. Figure 14.UN03Complete dominanceof one alleleRelationship amongalleles of a single geneDescription ExampleIncomplete dominanceof either alleleCodominanceMultiple allelesPleiotropyHeterozygous phenotypesame as that of homo-zygous dominantHeterozygous phenotypeintermediate betweenthe two homozygousphenotypesBoth phenotypesexpressed inheterozygotesIn the whole population,some genes have morethan two allelesOne gene is able to affectmultiple phenotypiccharactersABO blood group allelesSickle-cell diseasePP PpCRCRCRCWCWCWIAIBIA, IB, i
  98. 98. Figure 14.UN04EpistasisPolygenic inheritanceRelationship amongtwo or more genesDescription ExampleThe phenotypicexpression of onegene affects thatof anotherA single phenotypiccharacter is affectedby two or more genes9 : 3 : 4BbEe BbEeBEBEbEbEBeBebebeAaBbCc AaBbCc
  99. 99. Figure 14.UN05Flower positionStem lengthSeed shapeCharacter Dominant RecessiveAxial (A)Tall (T)Round (R)Terminal (a)Dwarf (t)Wrinkled (r)
  100. 100. Figure 14.UN06
  101. 101. Figure 14.UN07George ArleneSandra Tom Sam Wilma Ann MichaelCarlaDaniel Alan TinaChristopher
  102. 102. Figure 14.UN08
  103. 103. Figure 14.UN09
  104. 104. Figure 14.UN10
  105. 105. Figure 14.UN11
  106. 106. Figure 14.UN12
  107. 107. Figure 14.UN13
  108. 108. Figure 14.UN14

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