Sinh học - Chapter 8: The cellular basis of reproduction and inheritance

Chapter 8The Cellular Basis of Reproduction and Inheritance0Cancer cellsstart out as normal body cells,undergo genetic mutations,lose the ability to control the tempo of their own division, andrun amok, causing disease.0Introduction© 2012 Pearson Education, Inc.In a healthy body, cell division allows forgrowth,the replacement of damaged cells, anddevelopment from an embryo into an adult.In sexually reproducing organisms, eggs and sperm result frommitosis and meiosis.0Introduction© 2012 Pearson Education, Inc.Figure 8.0_2Chapter 8: Big IdeasCell Division andReproductionThe Eukaryotic CellCycle and MitosisMeiosis andCrossing OverAlterations of ChromosomeNumber and StructureFigure 8.0_3CELL DIVISION AND REPRODUCTION© 2012 Pearson Education, Inc.8.1 Cell division plays many important roles in the lives of organismsOrganisms reproduce their own kind, a key characteristic of life.Cell divisionis reproduction at the cellular level,requires the duplication of chromosomes, andsorts new sets of chromosomes into the resulting pair of daughter cells.0© 2012 Pearson Education, Inc.Cell division is usedfor reproduction of single-celled organisms,growth of multicellular organisms from a fertilized egg into an adult,repair and replacement of cells, andsperm and egg production.08.1 Cell division plays many important roles in the lives of organisms© 2012 Pearson Education, Inc.8.1 Cell division plays many important roles in the lives of organismsLiving organisms reproduce by two methods.Asexual reproductionproduces offspring that are identical to the original cell or organism andinvolves inheritance of all genes from one parent.Sexual reproductionproduces offspring that are similar to the parents, but show variations in traits andinvolves inheritance of unique sets of genes from two parents.0© 2012 Pearson Education, Inc.THE EUKARYOTIC CELL CYCLE AND MITOSIS© 2012 Pearson Education, Inc.Eukaryotic cellsare more complex and larger than prokaryotic cells,have more genes, andstore most of their genes on multiple chromosomes within the nucleus. 08.3 The large, complex chromosomes of eukaryotes duplicate with each cell division© 2012 Pearson Education, Inc.Eukaryotic chromosomes are composed of chromatin consisting ofone long DNA molecule andproteins that help maintain the chromosome structure and control the activity of its genes.To prepare for division, the chromatin becomeshighly compact andvisible with a microscope.08.3 The large, complex chromosomes of eukaryotes duplicate with each cell division© 2012 Pearson Education, Inc.Figure 8.3AFigure 8.3BSisterchromatidsChromosomesCentromereChromosomeduplicationSisterchromatidsChromosomedistributionto thedaughtercellsDNA moleculesBefore a eukaryotic cell begins to divide, it duplicates all of its chromosomes, resulting intwo copies called sister chromatidsjoined together by a narrowed “waist” called the centromere.When a cell divides, the sister chromatids separate from each other, now called chromosomes, and sort into separate daughter cells.08.3 The large, complex chromosomes of eukaryotes duplicate with each cell division© 2012 Pearson Education, Inc.Figure 8.3B_1ChromosomesCentromereChromosomeduplicationSisterchromatidsChromosomedistributionto thedaughtercellsDNA moleculesThe cell cycle is an ordered sequence of events that extendsfrom the time a cell is first formed from a dividing parent cell until its own division.08.4 The cell cycle multiplies cells© 2012 Pearson Education, Inc.The cell cycle consists of two stages, characterized as follows:Interphase: duplication of cell contentsG1—growth, increase in cytoplasmS—duplication of chromosomesG2—growth, preparation for divisionMitotic phase: divisionMitosis—division of the nucleusCytokinesis—division of cytoplasm08.4 The cell cycle multiplies cells© 2012 Pearson Education, Inc.Figure 8.4G1(first gap)S(DNA synthesis)G2(second gap)MCytokinesisMitosisINTERPHASEPHASETTMIOICMitosis progresses through a series of stages:prophase,prometaphase,metaphase,anaphase, andtelophase.Cytokinesis often overlaps telophase.08.5 Cell division is a continuum of dynamic changes© 2012 Pearson Education, Inc.Figure 8.5_1INTERPHASEMITOSISProphasePrometaphaseCentrosomeEarly mitoticspindleChromatinFragments ofthe nuclearenvelopeKinetochoreCentrosomes(with centriole pairs)CentriolesNuclearenvelopePlasmamembraneChromosome,consisting of twosister chromatidsCentromereSpindlemicrotubulesFigure 8.5_leftINTERPHASEMITOSISProphasePrometaphaseCentrosomeEarly mitoticspindleChromatinFragments ofthe nuclear envelopeKinetochoreCentrosomes(with centriole pairs)CentriolesNuclearenvelopePlasmamembraneChromosome,consisting of twosister chromatidsCentromereSpindlemicrotubulesA mitotic spindle isrequired to divide the chromosomes,composed of microtubules, andproduced by centrosomes, structures in the cytoplasm thatorganize microtubule arrangement andcontain a pair of centrioles in animal cells.08.5 Cell division is a continuum of dynamic changes© 2012 Pearson Education, Inc.InterphaseThe cytoplasmic contents double,two centrosomes form,chromosomes duplicate in the nucleus during the S phase, andnucleoli, sites of ribosome assembly, are visible.08.5 Cell division is a continuum of dynamic changes© 2012 Pearson Education, Inc.Figure 8.5_2INTERPHASEProphaseIn the cytoplasm microtubules begin to emerge from centrosomes, forming the spindle.In the nucleuschromosomes coil and become compact andnucleoli disappear.08.5 Cell division is a continuum of dynamic changes© 2012 Pearson Education, Inc.Figure 8.5_3ProphasePrometaphaseSpindle microtubules reach chromosomes, where theyattach at kinetochores on the centromeres of sister chromatids andmove chromosomes to the center of the cell through associated protein “motors.”Other microtubules meet those from the opposite poles.The nuclear envelope disappears.08.5 Cell division is a continuum of dynamic changes© 2012 Pearson Education, Inc.Figure 8.5_4PrometaphaseFigure 8.5_leftINTERPHASEMITOSISProphasePrometaphaseCentrosomeEarly mitoticspindleChromatinFragments ofthe nuclear envelopeKinetochoreCentrosomes(with centriole pairs)CentriolesNuclearenvelopePlasmamembraneChromosome,consisting of twosister chromatidsCentromereSpindlemicrotubulesFigure 8.5_5MITOSISAnaphaseMetaphaseTelophase and CytokinesisMetaphaseplateCleavagefurrowNuclearenvelopeformingDaughterchromosomesMitoticspindleFigure 8.5_rightMITOSISAnaphaseMetaphaseTelophase and CytokinesisMetaphaseplateCleavagefurrowNuclearenvelopeformingDaughterchromosomesMitoticspindleMetaphaseThe mitotic spindle is fully formed.Chromosomes align at the cell equator.Kinetochores of sister chromatids are facing the opposite poles of the spindle.08.5 Cell division is a continuum of dynamic changes© 2012 Pearson Education, Inc.Figure 8.5_6MetaphaseAnaphase Sister chromatids separate at the centromeres.Daughter chromosomes are moved to opposite poles of the cell asmotor proteins move the chromosomes along the spindle microtubules andkinetochore microtubules shorten.The cell elongates due to lengthening of nonkinetochore microtubules.08.5 Cell division is a continuum of dynamic changes© 2012 Pearson Education, Inc.Figure 8.5_7AnaphaseTelophaseThe cell continues to elongate.The nuclear envelope forms around chromosomes at each pole, establishing daughter nuclei.Chromatin uncoils and nucleoli reappear.The spindle disappears.08.5 Cell division is a continuum of dynamic changes© 2012 Pearson Education, Inc.Figure 8.5_8Telophase and CytokinesisFigure 8.5_rightMITOSISAnaphaseMetaphaseTelophase and CytokinesisMetaphaseplateCleavagefurrowNuclearenvelopeformingDaughterchromosomesMitoticspindleDuring cytokinesis, the cytoplasm is divided into separate cells.The process of cytokinesis differs in animal and plant cells.08.5 Cell division is a continuum of dynamic changes© 2012 Pearson Education, Inc.In animal cells, cytokinesis occurs asa cleavage furrow forms from a contracting ring of microfilaments, interacting with myosin, andthe cleavage furrow deepens to separate the contents into two cells.08.6 Cytokinesis differs for plant and animal cells© 2012 Pearson Education, Inc.Figure 8.6ACytokinesisCleavagefurrowContracting ring ofmicrofilamentsDaughtercellsCleavagefurrowIn plant cells, cytokinesis occurs asa cell plate forms in the middle, from vesicles containing cell wall material,the cell plate grows outward to reach the edges, dividing the contents into two cells,each cell now possesses a plasma membrane and cell wall.08.6 Cytokinesis differs for plant and animal cells© 2012 Pearson Education, Inc.Figure 8.6BCytokinesisCell wallof theparent cellDaughternucleusCell wallPlasmamembraneVesiclescontainingcell wallmaterialCell plateformingNewcell wallCell plateDaughtercellsThe cells within an organism’s body divide and develop at different rates.Cell division is controlled bythe presence of essential nutrients,growth factors, proteins that stimulate division,density-dependent inhibition, in which crowded cells stop dividing, andanchorage dependence, the need for cells to be in contact with a solid surface to divide.08.7 Anchorage, cell density, and chemical growthfactors affect cell division© 2012 Pearson Education, Inc.Figure 8.7ACultured cellssuspended in liquidThe addition ofgrowthfactorFigure 8.7BAnchorageSingle layerof cellsRemovalof cellsRestorationof singlelayer by celldivisionThe cell cycle control system is a cycling set of molecules in the cell thattriggers and coordinates key events in the cell cycle.Checkpoints in the cell cycle canstop an event orsignal an event to proceed. 08.8 Growth factors signal the cell cycle control system© 2012 Pearson Education, Inc.There are three major checkpoints in the cell cycle.G1 checkpointallows entry into the S phase orcauses the cell to leave the cycle, entering a nondividing G0 phase.G2 checkpoint, andM checkpoint.Research on the control of the cell cycle is one of the hottest areas in biology today.08.8 Growth factors signal the cell cycle control system© 2012 Pearson Education, Inc.Figure 8.8AG0G1 checkpointG1SMG2ControlsystemM checkpointG2 checkpointFigure 8.8BReceptorproteinSignaltransductionpathwayGrowthfactorRelay proteinsPlasma membraneEXTRACELLULAR FLUIDCYTOPLASMG1checkpointG1SMG2ControlsystemCancer currently claims the lives of 20% of the people in the United States and other industrialized nations.Cancer cells escape controls on the cell cycle.Cancer cellsdivide rapidly, often in the absence of growth factors,spread to other tissues through the circulatory system, andgrow without being inhibited by other cells.08.9 CONNECTION: Growing out of control, cancer cells produce malignant tumors© 2012 Pearson Education, Inc.A tumor is an abnormally growing mass of body cells. Benign tumors remain at the original site.Malignant tumors spread to other locations, called metastasis.08.9 CONNECTION: Growing out of control, cancer cells produce malignant tumors© 2012 Pearson Education, Inc.Figure 8.9TumorGlandulartissueGrowthInvasionMetastasisLymphvesselsBloodvesselTumor inanotherpart of the bodyCancers are named according to the organ or tissue in which they originate.Carcinomas arise in external or internal body coverings.Sarcomas arise in supportive and connective tissue.Leukemias and lymphomas arise from blood-forming tissues.08.9 CONNECTION: Growing out of control, cancer cells produce malignant tumors© 2012 Pearson Education, Inc.Cancer treatmentsLocalized tumors can beremoved surgically and/or treated with concentrated beams of high-energy radiation.Chemotherapy is used for metastatic tumors.08.9 CONNECTION: Growing out of control, cancer cells produce malignant tumors© 2012 Pearson Education, Inc.When the cell cycle operates normally, mitosis produces genetically identical cells forgrowth,replacement of damaged and lost cells, andasexual reproduction.08.10 Review: Mitosis provides for growth, cell replacement, and asexual reproduction© 2012 Pearson Education, Inc.Figure 8.10AMEIOSIS AND CROSSING OVER© 2012 Pearson Education, Inc.In humans, somatic cells have23 pairs of homologous chromosomes andone member of each pair from each parent.The human sex chromosomes X and Y differ in size and genetic composition.The other 22 pairs of chromosomes are autosomes with the same size and genetic composition.08.11 Chromosomes are matched in homologous pairs© 2012 Pearson Education, Inc.Homologous chromosomes are matched inlength,centromere position, andgene locations.A locus (plural, loci) is the position of a gene.Different versions of a gene may be found at the same locus on maternal and paternal chromosomes.08.11 Chromosomes are matched in homologous pairs© 2012 Pearson Education, Inc.Figure 8.11Pair of homologouschromosomesLocusCentromereSisterchromatidsOne duplicatedchromosomeAn organism’s life cycle is the sequence of stages leadingfrom the adults of one generationto the adults of the next.Humans and many animals and plants are diploid, with body cells that havetwo sets of chromosomes,one from each parent.08.12 Gametes have a single set of chromosomes© 2012 Pearson Education, Inc.Meiosis is a process that converts diploid nuclei to haploid nuclei.Diploid cells have two homologous sets of chromosomes.Haploid cells have one set of chromosomes.Meiosis occurs in the sex organs, producing gametes—sperm and eggs.Fertilization is the union of sperm and egg.The zygote has a diploid chromosome number, one set from each parent.08.12 Gametes have a single set of chromosomes© 2012 Pearson Education, Inc.Figure 8.12AHaploid gametes (n  23)Egg cellSperm cellFertilizationnnMeiosisOvaryTestisDiploidzygote(2n  46)2nMitosisKeyHaploid stage (n)Diploid stage (2n)Multicellular diploidadults (2n  46)All sexual life cycles include an alternation betweena diploid stage anda haploid stage.Producing haploid gametes prevents the chromosome number from doubling in every generation.08.12 Gametes have a single set of chromosomes© 2012 Pearson Education, Inc.Figure 8.12BA pair ofhomologouschromosomesin a diploidparent cellA pair ofduplicatedhomologouschromosomesSisterchromatids123INTERPHASEMEIOSIS IMEIOSIS IIMeiosis is a type of cell division that produces haploid gametes in diploid organisms.Two haploid gametes combine in fertilization to restore the diploid state in the zygote.08.13 Meiosis reduces the chromosome number from diploid to haploid© 2012 Pearson Education, Inc.Meiosis and mitosis are preceded by the duplication of chromosomes. However,meiosis is followed by two consecutive cell divisions andmitosis is followed by only one cell division.Because in meiosis, one duplication of chromosomes is followed by two divisions, each of the four daughter cells produced has a haploid set of chromosomes. 08.13 Meiosis reduces the chromosome number from diploid to haploid© 2012 Pearson Education, Inc.Meiosis I – Prophase I – events occurring in the nucleus.Chromosomes coil and become compact.Homologous chromosomes come together as pairs by synapsis.Each pair, with four chromatids, is called a tetrad.Nonsister chromatids exchange genetic material by crossing over.08.13 Meiosis reduces the chromosome number from diploid to haploid © 2012 Pearson Education, Inc.Figure 8.13_leftCentrosomes(with centriolepairs)CentriolesSites of crossing overSpindleTetradNuclearenvelopeChromatinSisterchromatidsFragmentsof thenuclearenvelopeCentromere(with akinetochore)Spindle microtubulesattached to a kinetochoreMetaphaseplateHomologouschromosomesseparateSister chromatidsremain attachedChromosomes duplicateProphase IMetaphase IAnaphase IINTERPHASE:MEIOSIS I: Homologous chromosomes separateMeiosis I – Metaphase I – Tetrads align at the cell equator.Meiosis I – Anaphase I – Homologous pairs separate and move toward opposite poles of the cell.08.13 Meiosis reduces the chromosome number from diploid to haploid © 2012 Pearson Education, Inc.Meiosis I – Telophase IDuplicated chromosomes have reached the poles.A nuclear envelope re-forms around chromosomes in some species.Each nucleus has the haploid number of chromosomes.08.13 Meiosis reduces the chromosome number from diploid to haploid © 2012 Pearson Education, Inc.Meiosis II follows meiosis I without chromosome duplication.Each of the two haploid products enters meiosis II.Meiosis II – Prophase IIChromosomes coil and become compact (if uncoiled after telophase I).Nuclear envelope, if re-formed, breaks up again. 08.13 Meiosis reduces the chromosome number from diploid to haploid © 2012 Pearson Education, Inc.Figure 8.13_rightCleavagefurrowTelophase I and CytokinesisProphase IIMetaphase IIAnaphase IIMEIOSIS II: Sister chromatids separateSister chromatidsseparateHaploid daughtercells formingTelophase IIand CytokinesisFigure 8.13_5Two lily cellsundergo meiosis IIMeiosis II – Metaphase II – Duplicated chromosomes align at the cell equator.Meiosis II – Anaphase IISister chromatids separate andchromosomes move toward opposite poles.08.13 Meiosis reduces the chromosome number from diploid to haploid © 2012 Pearson Education, Inc.Meiosis II – Telophase II Chromosomes have reached the poles of the cell.A nuclear envelope forms around each set of chromosomes.With cytokinesis, four haploid cells are produced.08.13 Meiosis reduces the chromosome number from diploid to haploid © 2012 Pearson Education, Inc.Mitosis and meiosis bothbegin with diploid parent cells that have chromosomes duplicated during the previous interphase. However the end products differ.Mitosis produces two genetically identical diploid somatic daughter cells.Meiosis produces four genetically unique haploid gametes.08.14 Mitosis and meiosis have important similarities and differences © 2012 Pearson Education, Inc.Figure 8.14ProphaseMetaphaseDuplicatedchromosome(two sisterchromatids)MITOSISParent cell(before chromosome duplication)ChromosomeduplicationChromosomeduplicationSite ofcrossingover2n  4Chromosomesalign at themetaphase plateTetrads (homologouspairs) align at themetaphase plateTetrad formedby synapsis ofhomologouschromosomesMetaphase IProphase IMEIOSIS IAnaphaseTelophaseSister chromatidsseparate duringanaphase2n2nDaughter cells of mitosisNo furtherchromosomalduplication;sisterchromatidsseparate duringanaphase IInnnnDaughter cells of meiosis IIDaughtercells ofmeiosis IHaploidn  2Anaphase ITelophase IHomologouschromosomesseparate duringanaphase I;sisterchromatidsremain togetherMEIOSIS IIFigure 8.14_1ProphaseMetaphaseMITOSISParent cell(before chromosome duplication)ChromosomeduplicationChromosomeduplicationSite ofcrossingover2n  4Chromosomesalign at themetaphase plateTetrads (homologouspairs) align at themetaphase plateTetradMetaphase IProphase IMEIOSIS IFigure 8.14_2MetaphaseMITOSISChromosomesalign at themetaphase plateAnaphaseTelophaseSister chromatidsseparate duringanaphase2n2nDaughter cells of mitosisFigure 8.14_3Tetrads (homologouspairs) align at themetaphase plateMetaphase INo furtherchromosomalduplication;sisterchromatidsseparate duringanaphase IInDaughter cells of meiosis IIDaughtercells ofmeiosis IHaploidn  2Anaphase ITelophase IHomologouschromosomesseparate duringanaphase I;sisterchromatidsremain togetherMEIOSIS IIMEIOSIS InnnGenetic variation in gametes results fromindependent orientation at metaphase I andrandom fertilization.08.15 Independent orientation of chromosomes in meiosis and random fertilization lead to varied offspring© 2012 Pearson Education, Inc.Independent orientation at metaphase IEach pair of chromosomes independently aligns at the cell equator.There is an equal probability of the maternal or paternal chromosome facing a given pole.The number of combinations for chromosomes packaged into gametes is 2n where n = haploid number of chromosomes.08.15 Independent orientation of chromosomes in meiosis and random fertilization lead to varied offspring© 2012 Pearson Education, Inc.Random fertilization – The combination of each unique sperm with each unique egg increases genetic variability.08.15 Independent orientation of chromosomes in meiosis and random fertilization lead to varied offspring© 2012 Pearson Education, Inc.Figure 8.15_s1Possibility ATwo equally probablearrangements ofchromosomes atmetaphase IPossibility BFigure 8.15_s2Possibility ATwo equally probablearrangements ofchromosomes atmetaphase IPossibility BMetaphase IIFigure 8.15_s3Possibility ATwo equally probablearrangements ofchromosomes atmetaphase IPossibility BMetaphase IIGametesCombination 3Combination 4Combination 2Combination 18.16 Homologous chromosomes may carry different versions of genesSeparation of homologous chromosomes during meiosis can lead to genetic differences between gametes.Homologous chromosomes may have different versions of a gene at the same locus.One version was inherited from the maternal parent and the other came from the paternal parent.Since homologues move to opposite poles during anaphase I, gametes will receive either the maternal or paternal version of the gene.© 2012 Pearson Education, Inc.Figure 8.16Coat-colorgenesEye-colorgenesBrownBlackMeiosisWhitePinkTetrad in parent cell(homologous pair ofduplicated chromosomes)Chromosomes ofthe four gametesWhite coat (c);pink eyes (e)Brown coat (C);black eyes (E)ECeceEEeccCCGenetic recombination is the production of new combinations of genes due to crossing over.Crossing over is an exchange of corresponding segments between separate (nonsister) chromatids on homologous chromosomes.Nonsister chromatids join at a chiasma (plural, chiasmata), the site of attachment and crossing over.Corresponding amounts of genetic material are exchanged between maternal and paternal (nonsister) chromatids.08.17 Crossing over further increases genetic variability© 2012 Pearson Education, Inc.Figure 8.17AChiasmaTetradFigure 8.17B_1Tetrad(pair of homologouschromosomes in synapsis)Breakage of homologous chromatidsJoining of homologous chromatids12CceECceECceEChiasmaFigure 8.17B_2Separation of homologouschromosomes at anaphase I3CECeChiasmaccEeCEceFigure 8.17B_3Separation of chromatids atanaphase II andcompletion of meiosisParental type of chromosomeRecombinant chromosomeRecombinant chromosomeParental type of chromosomeGametes of four genetic typesCEeC4EcceECeCcEce ALTERATIONS OF CHROMOSOME NUMBER AND STRUCTURE© 2012 Pearson Education, Inc.A karyotype is an ordered display of magnified images of an individual’s chromosomes arranged in pairs.Karyotypesare often produced from dividing cells arrested at metaphase of mitosis andallow for the observation of homologous chromosome pairs,chromosome number, andchromosome structure.08.18 A karyotype is a photographic inventory of an individual’s chromosomes© 2012 Pearson Education, Inc.Figure 8.18_s5CentromereSisterchromatidsPair ofhomologouschromosomes5Sex chromosomesTrisomy 21involves the inheritance of three copies of chromosome 21 andis the most common human chromosome abnormality.08.19 CONNECTION: An extra copy of chromosome 21 causes Down syndrome© 2012 Pearson Education, Inc.Trisomy 21, called Down syndrome, produces a characteristic set of symptoms, which include: mental retardation,characteristic facial features,short stature,heart defects,susceptibility to respiratory infections, leukemia, and Alzheimer’s disease, andshortened life span.The incidence increases with the age of the mother.08.19 CONNECTION: An extra copy of chromosome 21 causes Down syndrome© 2012 Pearson Education, Inc.Figure 8.19ATrisomy 21Figure 8.19BAge of mother504540353025200102030405060708090Infants with Down syndrome(per 1,000 births)Nondisjunction is the failure of chromosomes or chromatids to separate normally during meiosis. This can happen duringmeiosis I, if both members of a homologous pair go to one pole ormeiosis II if both sister chromatids go to one pole.Fertilization after nondisjunction yields zygotes with altered numbers of chromosomes.08.20 Accidents during meiosis can alter chromosome number© 2012 Pearson Education, Inc.Figure 8.20A_s1NondisjunctionMEIOSIS IFigure 8.20A_s2NondisjunctionMEIOSIS IMEIOSIS IINormalmeiosis IIFigure 8.20A_s3NondisjunctionMEIOSIS IMEIOSIS IINormalmeiosis IIGametesNumber ofchromosomesAbnormal gametesn  1n  1n  1n  1Figure 8.20B_s1Normalmeiosis IMEIOSIS IFigure 8.20B_s2Normalmeiosis IMEIOSIS IMEIOSIS IINondisjunctionFigure 8.20B_s3Normalmeiosis IMEIOSIS IMEIOSIS IINondisjunctionAbnormal gametesNormal gametesn  1n  1nnSex chromosome abnormalities tend to be less severe, perhaps because ofthe small size of the Y chromosome orX-chromosome inactivation.08.21 CONNECTION: Abnormal numbers of sexchromosomes do not usually affect survival© 2012 Pearson Education, Inc.Chromosome breakage can lead to rearrangements that can produce genetic disorders or, if changes occur in somatic cells, cancer.08.23 CONNECTION: Alterations of chromosome structure can cause birth defects and cancer© 2012 Pearson Education, Inc.These rearrangements may includea deletion, the loss of a chromosome segment,a duplication, the repeat of a chromosome segment,an inversion, the reversal of a chromosome segment, ora translocation, the attachment of a segment to a nonhomologous chromosome that can be reciprocal.08.23 CONNECTION: Alterations of chromosome structure can cause birth defects and cancer© 2012 Pearson Education, Inc.Chronic myelogenous leukemia (CML)is one of the most common leukemias,affects cells that give rise to white blood cells (leukocytes), andresults from part of chromosome 22 switching places with a small fragment from a tip of chromosome 9.08.23 CONNECTION: Alterations of chromosome structure can cause birth defects and cancer© 2012 Pearson Education, Inc.Figure 8.23ADeletionDuplicationInversionReciprocal translocationHomologouschromosomesNonhomologouschromosomesFigure 8.23BChromosome 9Chromosome 22Reciprocaltranslocation“Philadelphia chromosome”Activated cancer-causing gene