Chapter 14- Human Genetics

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Sex-linked traits, chromosome disorders, and more!

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<ul><li> 1. BiologyCopyright Pearson Prentice HallBiology</li></ul><p> 2. 141 Human Heredity 14-1 Human HeredityCopyright Pearson Prentice Hall 3. Human ChromosomesCell biologists analyze chromosomes bylooking at karyotypes.Cells are photographed during mitosis.Scientiststhen cut out thechromosomesfrom thephotographsand group themtogether inpairs.Copyright Pearson Prentice Hall 4. A picture of an individualschromosomes, arranged inhomologous pairs, is called akaryotype.Copyright Pearson Prentice HallHumanKaryotype 5. Human ChromosomesHumans have 46 chromosomes.Two are called sex chromosomes,because they determine anindividual's sex.Females have two Xchromosomes.Males have one X chromosomeand one Y chromosome.Copyright Pearson Prentice Hall 6. Human ChromosomesThe other 44 chromosomes areknown as autosomal chromosomes,or autosomes.Copyright Pearson Prentice Hall 7. Human ChromosomesAll human egg cells carry asingle X chromosome (23,X).Half of all sperm cells carry anX chromosome (23,X) and halfcarry a Y chromosome (23,Y).About half of the zygotes will be 46,XX(female) and half will be 46,XY (male).Copyright Pearson Prentice Hall 8. Human ChromosomesMales andfemales areborn in aroughly 50 : 50ratio becauseof the way inwhich sexchromosomessegregateduring meiosis.Copyright Pearson Prentice Hall 9. Copyright Pearson Prentice Hall 10. Human TraitsHuman TraitsIn order to apply Mendelian genetics tohumans, biologists must identify aninherited trait controlled by a single gene.They must establish that the trait isinherited and not the result ofenvironmental influences.They have to study how the trait ispassed from one generation to the next.Copyright Pearson Prentice Hall 11. Human TraitsPedigree ChartsA pedigree chart shows therelationships within a family.Genetic counselors analyze pedigreecharts to infer the genotypes of familymembers.Copyright Pearson Prentice HallActive art 12. Human TraitsA circlerepresentsa female.A horizontal lineconnecting a male and afemale represents amarriage.Copyright Pearson Prentice HallA shadedcircle orsquareindicates that apersonexpresses thetrait.A squarerepresentsa male.A vertical line anda bracket connectthe parents to theirchildren.A circle or square that isnot shaded indicates thata person does not expressthe trait. 13. Genes and the EnvironmentSome obvious human traits are almostimpossible to associate with single genes.Traits, such as the shape of youreyes or ears, are polygenic,meaning they are controlled bymany genes.Many of your personal traits are onlypartly governed by genetics.Copyright Pearson Prentice Hall 14. Human GenesThe human genome includes tens ofthousands of genes.In 2003, the DNA sequence of the humangenome was published.In a few cases, biologists were able toidentify genes that directly control asingle human trait such as blood type.Copyright Pearson Prentice Hall 15. Blood Group GenesHuman blood comes in a variety ofgenetically determined blood groups.A number of genes are responsible forhuman blood groups.The best known are the ABO bloodgroups and the Rh blood groups.Copyright Pearson Prentice Hall 16. Human GenesThe Rh blood group is determined by a singlegene with two allelespositive and negative.The positive (Rh+) allele isdominant, so individuals who areRh+/Rh+ or Rh+/Rh are said to beRh-positive.Individuals with two Rh- alleles aresaid to be Rh-negative.Copyright Pearson Prentice Hall 17. Human GenesABO blood groupThere are three alleles for thisgene, IA, IB, and i.Alleles IA and IB are codominant.Copyright Pearson Prentice Hall 18. Human GenesIndividuals with alleles IA and IBproduce both A and B antigens,making them blood type AB.Copyright Pearson Prentice Hall 19. Human GenesThe i allele is recessive.Individuals with alleles IAIA or IAiproduce only the A antigen,making them blood type A.Copyright Pearson Prentice Hall 20. Human GenesIndividuals with IBIB or IBi allelesare type B.Copyright Pearson Prentice Hall 21. Human GenesIndividuals who are homozygousfor the i allele (ii) produce noantigen and are said to haveblood type O.Copyright Pearson Prentice Hall 22. Copyright Pearson Prentice Hall 23. Recessive AllelesThe presence of a normal, functioninggene is revealed only when an abnormalor nonfunctioning allele affects thephenotype.Many disorders are caused byautosomal recessive alleles.Copyright Pearson Prentice Hall 24. Copyright Pearson Prentice Hall 25. Dominant AllelesThe effects of a dominant alleleare expressed even when therecessive allele is present.Two examples of genetic disorderscaused by autosomal dominant allelesare achondroplasia and Huntingtondisease.Copyright Pearson Prentice Hall 26. Copyright Pearson Prentice Hall 27. Codominant AllelesSickle cell disease is a seriousdisorder caused by acodominant allele.Sickle cell is found in about 1 out of 500African Americans.Copyright Pearson Prentice Hall 28. Copyright Pearson Prentice Hall 29. Sickle Cell Disease ischaracterized by thebent and twistedshape of the redblood cells.Copyright Pearson Prentice Hall 30. Hemoglobin is the protein in red bloodcells that carries oxygen.In the sickle cell allele, just one DNA baseis changed.As a result, the abnormal hemoglobin isless soluble than normal hemoglobin.Low oxygen levels cause some red bloodcells to become sickle shaped.Copyright Pearson Prentice Hall 31. There are three phenotypes associatedwith the sickle cell gene.Homozygous dominant- normalHeterozygous dominant- healthywith malaria resistanceHomozygous recessive- sickle cellSickle cell alleles areconsidered codominant.Copyright Pearson Prentice Hall 32. Malaria and the Sickle Cell AlleleRegions where malaria iscommonRegions where the sicklecell allele is commonBecause the sickle cell allele givesresistance to malaria it persists inareas where malaria is a problem.Copyright Pearson Prentice Hall 33. In both cystic fibrosis and sicklecell disease, a small change in theDNA of a single gene affects thestructure of a protein, causing aserious genetic disorder.Copyright Pearson Prentice Hall 34. From Gene to MoleculeCystic FibrosisCystic fibrosis is caused by arecessive allele.Sufferers of cystic fibrosis produce athick, heavy mucus that clogs their lungsand breathing passageways.Copyright Pearson Prentice Hall 35. The mostcommon allelethat causescystic fibrosis ismissing 3 DNAbases.As a result, theamino acidphenylalanine ismissing from theCFTR protein.Copyright Pearson Prentice Hall 36. From Gene to MoleculeNormal CFTR is achloride ionchannel in cellmembranes.Abnormal CFTRcannot betransported to thecell membrane.Copyright Pearson Prentice Hall 37. The cells in thepersons airwaysare unable totransport chlorideions.As a result, theairways becomeclogged with athick mucus.Copyright Pearson Prentice Hall 38. These diseases are autosomalrecessive because you only needone functional gene to make a goodprotein.FF Ff ffCopyright Pearson Prentice HallMakesgoodproteinMakes somegood proteinand some thatdoesnt workMakes proteinthat doesntwork 39. 142 Human Chromosomes14-2 Human ChromosomesCopyright Pearson Prentice Hall 40. Sex-Linked GenesThe X chromosome and the Ychromosomes determine sex.Genes located on sexchromosomes are called sex-linkedgenes.More than 100 sex-linked geneticdisorders have now been mapped to theX chromosome.Copyright Pearson Prentice Hall 41. Sex-Linked GenesThe Ychromosome ismuch smallerthan the Xchromosomeand appears tocontain only afew genes.X ChromosomeCopyright Pearson Prentice HallDuchenne musculardystrophyMelanomaX-inactivation centerX-linked severe combinedimmunodeficiency (SCID)ColorblindnessHemophiliaY ChromosomeTestis-determiningfactor 42. For a recessive allele to be expressed infemales, there must be two copies of theallele, one on each of the two Xchromosomes.Males have just one Xchromosome. Thus, all X-linkedalleles are expressed inmales, even if they arerecessive.Copyright Pearson Prentice Hall 43. ColorblindnessThree human genes associated with colorvision are located on the X chromosome.In males, adefective versionof any one ofthese genesproducescolorblindness.Copyright Pearson Prentice Hall 44. Copyright Pearson Prentice HallPossibleInheritance ofColorblindnessAllele 45. HemophiliaThe X chromosome also carries genesthat help control blood clotting. Arecessive allele in either of these twogenes may produce hemophilia. In hemophilia, a protein necessary fornormal blood clotting is missing.Hemophiliacs can bleed to death fromcuts and may suffer internal bleeding ifbruised.Copyright Pearson Prentice Hall 46. Duchenne Muscular DystrophyDuchenne muscular dystrophy is a sex-linkeddisorder that results in theweakening and loss of skeletal muscle. It is caused by a defective version of thegene that codes for a muscle protein.Copyright Pearson Prentice Hall 47. Recessive traits from geneson the X-chromosome, likecolor blindness andhemophilia,are muchmorecommonin males. 48. X-Chromosome InactivationBritish geneticist Mary Lyon discovered thatin female cells, one X chromosome israndomly switched off.The inactive X chromosome forms adense region in the nucleus known asa Barr body. Barr bodies are generallynot found in males becausetheir single X chromosomeis still active.Copyright Pearson Prentice Hall 49. GENETIC DISORDERS caused byNON-DISJUNCTIONThe most common error in meiosisoccurs when homologouschromosomes fail to separate.Copyright Pearson Prentice Hall 50. GENETIC DISORDERS caused byNON-DISJUNCTIONCopyright Pearson Prentice Hall 51. GENETIC DISORDERS caused byNON-DISJUNCTIONThis is known as nondisjunction,which means, not coming apart.nondisjunction causes abnormalnumbers of chromosomesCopyright Pearson Prentice Hall 52. Down SyndromeIf two copies of an autosomalchromosome fail to separateduring meiosis, an individualmay be born with three copiesof a chromosome.Down syndrome involves threecopies of chromosome 21.Copyright Pearson Prentice Hall 53. Chromosomal DisordersDown syndromeproduces mild tosevere mentalretardation.It is characterized by: increasedsusceptibility tomany diseaseshigher frequencyof some birthdefectsDown Syndrome KaryotypeCopyright Pearson Prentice Hall 54. Sex Chromosome Disorders In females, nondisjunction can leadto Turners syndrome.A female with Turners syndromeusually inherits only one Xchromosome (karyotype 45,X).Women with Turners syndrome aresterile.Copyright Pearson Prentice Hall 55. Chromosomal DisordersIn males, nondisjunction causesKlinefelters syndrome (karyotype 47,XXY).The extra X chromosome interferes withmeiosis and usually prevents theseindividuals from reproducing.Copyright Pearson Prentice Hall 56. The X chromosome contains genesnecessary for survival. 57. 143 Human Molecular Genetics 14-3 Human Molecular GeneticsCopyright Pearson Prentice Hall 58. Human DNA Analysis There are roughly 6 billion base pairs inyour DNA.Biologists search the human genomeusing sequences of DNA bases.Copyright Pearson Prentice Hall 59. Genetic tests are available for hundreds ofdisorders.DNA testing can pinpoint the exactgenetic basis of a disorder.Copyright Pearson Prentice Hall 60. DNA fingerprinting analyzes theDNA repeats which make a uniquepattern for each individual.Only identical twins are geneticallyidentical.DNA samples can be obtained from blood,sperm, and hair strands with tissue at thebase.Copyright Pearson Prentice Hall 61. Human DNA AnalysisChromosomescontain largeamounts ofDNA calledrepeats that donot code forproteins.This DNA patternvaries from personto person.Copyright Pearson Prentice HallActive art 62. Restriction enzymes are used to cut theDNA into fragments containing genes andrepeats.Copyright Pearson Prentice Hall 63. DNA fragmentsare separatedusing gelelectrophoresis.Fragmentscontaining repeatsare labeled.This produces aseries of bandsthe DNAfingerprint.Copyright Pearson Prentice Hall 64. Copyright Pearson Prentice HallDNA Fingerprint 65. In 1990, scientists in the United Statesand other countries began the HumanGenome Project.The Human Genome Project isan ongoing effort to analyze thehuman DNA sequence.In June 2000, a working copy of thehuman genome was essentiallycomplete.Copyright Pearson Prentice Hall 66. Research groups are analyzing the DNAsequence, looking for genes that mayprovide clues to the basic properties of life.Biotechnology companies are looking forinformation that may help develop newdrugs and treatments for diseases.Copyright Pearson Prentice Hall 67. A Breakthrough for EveryoneData from publicly supported researchon the human genome have beenposted on the Internet on a daily basis.You can read and analyze the latestgenome data.Copyright Pearson Prentice Hall 68. In gene therapy, an absent orfaulty gene is replaced by anormal, working gene.The body can then make the correctprotein or enzyme, eliminating the causeof the disorder.Copyright Pearson Prentice Hall 69. Viruses are oftenused because oftheir ability to entera cells DNA.Virus particles aremodified so that theycannot causedisease.Normal hemoglobin geneGenetically engineered virusCopyright Pearson Prentice Hall 70. A DNA fragment containing a replacementgene is spliced to viral DNA.Bone marrow cellCopyright Pearson Prentice HallChromosomesNucleusGenetically engineered virus 71. The patient is then infected with themodified virus particles, which shouldcarry the gene into cells to correct geneticdefects.Copyright Pearson Prentice Hall 72. Copyright Pearson Prentice Hall141A chromosome that is not a sex chromosome isknow as a(an)a. autosome.b. karyotype.c. pedigree.d. chromatid. 73. Copyright Pearson Prentice Hall141Whether a human will be a male or a female isdetermined by whicha. sex chromosome is in the egg cell.b. autosomes are in the egg cell.c. sex chromosome is in the sperm cell.d. autosomes are in the sperm cell. 74. Copyright Pearson Prentice Hall141Mendelian inheritance in humans is typicallystudied bya. making inferences from familypedigrees.b. carrying out carefully controlledcrosses.c. observing the phenotypes of individualhumans.d. observing inheritance patterns in otheranimals. 75. Copyright Pearson Prentice Hall141An individual with a blood type phenotype of Ocan receive blood from an individual with thephenotypea. O.b. A.c. AB.d. B. 76. Copyright Pearson Prentice Hall141The ABO blood group is made up ofa. two alleles.b. three alleles.c. identical alleles.d. dominant alleles. 77. Copyright Pearson Prentice Hall142The average human gene consists of how manybase pairs of DNA?a. 3000b. 300c. 20d. 30,000 78. Copyright Pearson Prentice Hall142Which of the following genotypes indicates anindividual who is a carrier for colorblindness?a. XCXb. XCXcc. XcYd. XCY 79. Copyright Pearson Prentice Hall142Colorblindness is much more common in malesthan in females becausea. the recessive gene on the males single Xchromosome is expressed.b. genes on the Y chromosome make genes onthe X chromosome more active.c. females cannot be colorblind.d. colorblindness is dominant in males andrecessive in females. 80....</p>