Sinh học - Chapter 9: Patterns of inheritance

Chapter 9Patterns of Inheritance0Dogs are one of man’s longest genetic experiments.Over thousands of years, humans have chosen and mated dogs with specific traits.The result has been an incredibly diverse array of dogs with distinctbody types and behavioral traits.0Introduction© 2012 Pearson Education, Inc.Figure 9.0_1Chapter 9: Big IdeasMendel’s LawsVariations onMendel’s LawsThe Chromosomal Basisof InheritanceSex Chromosomes andSex-Linked GenesMENDEL’S LAWS© 2012 Pearson Education, Inc.9.1 The science of genetics has ancient rootsPangenesis, proposed around 400 BCE by Hippocrates, was an early explanation for inheritance that suggested thatparticles called pangenes came from all parts of the organism to be incorporated into eggs or sperm and characteristics acquired during the parents’ lifetime could be transferred to the offspring.Aristotle rejected pangenesis and argued that instead of particles, the potential to produce the traits was inherited.0© 2012 Pearson Education, Inc.9.1 The science of genetics has ancient rootsThe idea that hereditary materials mix in forming offspring, called the blending hypothesis, wassuggested in the 19th century by scientists studying plants butlater rejected because it did not explain how traits that disappear in one generation can reappear in later generations.0© 2012 Pearson Education, Inc.9.2 Experimental genetics began in an abbey gardenHeredity is the transmission of traits from one generation to the next.Genetics is the scientific study of heredity.Gregor Mendelbegan the field of genetics in the 1860s,deduced the principles of genetics by breeding garden peas, andrelied upon a background of mathematics, physics, and chemistry.0© 2012 Pearson Education, Inc.9.2 Experimental genetics began in an abbey gardenIn 1866, Mendelcorrectly argued that parents pass on to their offspring discrete “heritable factors” and stressed that the heritable factors (today called genes), retain their individuality generation after generation.A heritable feature that varies among individuals, such as flower color, is called a character.Each variant for a character, such as purple or white flowers, is a trait.0© 2012 Pearson Education, Inc.9.2 Experimental genetics began in an abbey gardenTrue-breeding varieties result when self-fertilization produces offspring all identical to the parent.The offspring of two different varieties are hybrids.The cross-fertilization is a hybridization, or genetic cross.True-breeding parental plants are the P generation.Hybrid offspring are the F1 generation.A cross of F1 plants produces an F2 generation.0© 2012 Pearson Education, Inc.Figure 9.2BStamenCarpelPetalFigure 9.2C_s1Removal ofstamensCarpelWhiteStamensTransferof pollenPurpleParents(P)21Figure 9.2C_s2Removal ofstamensCarpelWhiteStamensTransferof pollenPurpleCarpel maturesinto pea podParents(P)231Figure 9.2C_s3Removal ofstamensCarpelWhiteStamensTransferof pollenPurpleCarpel maturesinto pea podSeeds frompod plantedOffspring(F1)Parents(P)2314Figure 9.2DCharacterTraitsDominantRecessiveFlower colorPurpleWhiteFlower positionAxialTerminalSeed colorYellowGreenSeed shapeRoundWrinkledPod shapeInflatedConstrictedPod colorGreenYellowStem lengthTallDwarf9.3 Mendel’s law of segregation describes the inheritance of a single characterA cross between two individuals differing in a single character is a monohybrid cross.Mendel performed a monohybrid cross between a plant with purple flowers and a plant with white flowers.The F1 generation produced all plants with purple flowers.A cross of F1 plants with each other produced an F2 generation with ¾ purple and ¼ white flowers.0© 2012 Pearson Education, Inc.Figure 9.3A_s1The ExperimentP generation(true-breedingparents)PurpleflowersWhiteflowersFigure 9.3A_s2The ExperimentP generation(true-breedingparents)F1 generationPurpleflowersWhiteflowersAll plants havepurple flowersFigure 9.3A_s3The ExperimentP generation(true-breedingparents)F1 generationF2 generation of plantshave purple flowers of plantshave white flowersPurpleflowersWhiteflowersAll plants havepurple flowersFertilizationamong F1 plants(F1  F1)34149.3 Mendel’s law of segregation describes the inheritance of a single characterThe all-purple F1 generation did not produce light purple flowers, as predicted by the blending hypothesis.Mendel needed to explain whywhite color seemed to disappear in the F1 generation andwhite color reappeared in one quarter of the F2 offspring.Mendel observed the same patterns of inheritance for six other pea plant characters.0© 2012 Pearson Education, Inc.9.3 Mendel’s law of segregation describes the inheritance of a single characterMendel developed four hypotheses, described below using modern terminology.1. Alleles are alternative versions of genes that account for variations in inherited characters.2. For each characteristic, an organism inherits two alleles, one from each parent. The alleles can be the same or different.A homozygous genotype has identical alleles.A heterozygous genotype has two different alleles.0© 2012 Pearson Education, Inc.9.3 Mendel’s law of segregation describes the inheritance of a single characterIf the alleles of an inherited pair differ, then one determines the organism’s appearance and is called the dominant allele. The other has no noticeable effect on the organism’s appearance and is called the recessive allele.The phenotype is the appearance or expression of a trait.The genotype is the genetic makeup of a trait.The same phenotype may be determined by more than one genotype.0© 2012 Pearson Education, Inc.9.3 Mendel’s law of segregation describes the inheritance of a single characterA sperm or egg carries only one allele for each inherited character because allele pairs separate (segregate) from each other during the production of gametes. This statement is called the law of segregation.Mendel’s hypotheses also explain the 3:1 ratio in the F2 generation.The F1 hybrids all have a Pp genotype.A Punnett square shows the four possible combinations of alleles that could occur when these gametes combine.0© 2012 Pearson Education, Inc.Figure 9.3B_s1The ExplanationP generationGenetic makeup (alleles)Purple flowersWhite flowersGametesAll pppPPPAllFigure 9.3B_s2The ExplanationP generationF1 generation(hybrids)Genetic makeup (alleles)Purple flowersWhite flowersGametesAll pppPPPpGametesAll Pp2121PAllFigure 9.3B_s3The ExplanationP generationF1 generation(hybrids)F2 generationGenetic makeup (alleles)Purple flowersWhite flowersGametesPAll pppPPPPPpppPPPpPpppEggsfrom F1 plantGametesFertilizationAll PpAllelessegregatePhenotypic ratio3 purple : 1 whiteGenotypic ratio1 PP : 2 Pp : 1 ppSperm from F1 plant2121AllFigure 9.3B_4F2 generationPPppPPPpPpppEggsfrom F1 plantPhenotypic ratio3 purple : 1 whiteGenotypic ratio1 PP : 2 Pp : 1 ppSperm from F1 plant9.4 Homologous chromosomes bear the alleles for each characterA locus (plural, loci) is the specific location of a gene along a chromosome.For a pair of homologous chromosomes, alleles of a gene reside at the same locus.Homozygous individuals have the same allele on both homologues.Heterozygous individuals have a different allele on each homologue.0© 2012 Pearson Education, Inc.Figure 9.4PPaaBbPPaaBbDominantalleleRecessivealleleGene lociHomologouschromosomesGenotype:Heterozygous,with one dominantand one recessivealleleHomozygousfor the recessivealleleHomozygousfor the dominantallele9.5 The law of independent assortment is revealed by tracking two characters at onceA dihybrid cross is a mating of parental varieties that differ in two characters.Mendel performed the following dihybrid cross with the following results:P generation: round yellow seeds  wrinkled green seeds F1 generation: all plants with round yellow seeds F2 generation:9/16 had round yellow seeds3/16 had wrinkled yellow seeds3/16 had round green seeds1/16 had wrinkled green seeds0© 2012 Pearson Education, Inc.Figure 9.5A414141414141414116916316316121212121F1 generationF2 generationP generationGametesSpermEggsYellowroundGreenroundYellowwrinkledGreenwrinkledRRYYrryyRYryRrYyThe hypothesis of dependent assortmentData did not support; hypothesis refutedThe hypothesis of independent assortmentActual results; hypothesis supportedRYRYryryEggsRYRYrYrYRyRyryryRRYYRrYYRRYyRrYyRrYYrrYYRrYyrrYyRRYyRrYyRRyyRryyRrYyrrYyRryyrryySpermFigure 9.5BPhenotypesGenotypesBlack coat,normal visionB_N_Black coat,blind (PRA)B_nnBlindChocolate coat,normal visionbbN_BlindBlindBlindChocolate coat,blind (PRA)bbnnMating of double heterozygotes (black coat, normal vision)BbNnBbNnPhenotypic ratioof the offspring9Black coat,normal vision3Black coat,blind (PRA)1Chocolate coat,blind (PRA)3Chocolate coat,normal vision9.5 The law of independent assortment is revealed by tracking two characters at onceMendel needed to explain why the F2 offspringhad new nonparental combinations of traits anda 9:3:3:1 phenotypic ratio.Mendelsuggested that the inheritance of one character has no effect on the inheritance of another,suggested that the dihybrid cross is the equivalent to two monohybrid crosses, andcalled this the law of independent assortment.0© 2012 Pearson Education, Inc.9.5 The law of independent assortment is revealed by tracking two characters at onceThe following figure demonstrates the law of independent assortment as it applies to two characters in Labrador retrievers:black versus chocolate color,normal vision versus progressive retinal atrophy.0© 2012 Pearson Education, Inc.9.6 Geneticists can use the testcross to determine unknown genotypesA testcross is the mating between an individual of unknown genotype and a homozygous recessive individual.A testcross can show whether the unknown genotype includes a recessive allele.Mendel used testcrosses to verify that he had true-breeding genotypes.The following figure demonstrates how a testcross can be performed to determine the genotype of a Lab with normal eyes.0© 2012 Pearson Education, Inc.Figure 9.6What is the genotype of the black dog?Two possibilities for the black dog:TestcrossGenotypesGametesOffspringAll black1 black : 1 chocolateorB_?bbBbBBBBbbbBbBbbb9.7 Mendel’s laws reflect the rules of probabilityUsing his strong background in mathematics, Mendel knew that the rules of mathematical probability affectedthe segregation of allele pairs during gamete formation and the re-forming of pairs at fertilization.The probability scale ranges from 0 to 1. An event that iscertain has a probability of 1 andcertain not to occur has a probability of 0.0© 2012 Pearson Education, Inc.9.7 Mendel’s laws reflect the rules of probabilityThe probability of a specific event is the number of ways that event can occur out of the total possible outcomes.Determining the probability of two independent events uses the rule of multiplication, in which the probability is the product of the probabilities for each event.The probability that an event can occur in two or more alternative ways is the sum of the separate probabilities, called the rule of addition.0© 2012 Pearson Education, Inc.Figure 9.7F1 genotypesFormationof eggsFormationof spermBb femaleBb maleSpermF2 genotypesEggsBBBBBBbbbbbb21212121212141414141( )9.8 CONNECTION: Genetic traits in humans can be tracked through family pedigreesIn a simple dominant-recessive inheritance of dominant allele A and recessive allele a,a recessive phenotype always results from a homozygous recessive genotype (aa) buta dominant phenotype can result from eitherthe homozygous dominant genotype (AA) ora heterozygous genotype (Aa).Wild-type traits, those prevailing in nature, are not necessarily specified by dominant alleles.0© 2012 Pearson Education, Inc.Figure 9.8ADominant TraitsRecessive TraitsFrecklesNo frecklesWidow’s peakStraight hairlineFree earlobeAttached earlobe9.8 CONNECTION: Genetic traits in humans can be tracked through family pedigreesThe inheritance of human traits follows Mendel’s laws.A pedigreeshows the inheritance of a trait in a family through multiple generations,demonstrates dominant or recessive inheritance, andcan also be used to deduce genotypes of family members.0© 2012 Pearson Education, Inc.Figure 9.8BFirst generation(grandparents)Second generation(parents, aunts,and uncles)Third generation(two sisters)FemaleMaleAttachedFreeFfFfFfffFfFfffffffffFForFfFForFf9.9 CONNECTION: Many inherited disorders in humans are controlled by a single geneInherited human disorders show eitherrecessive inheritance in whichtwo recessive alleles are needed to show disease,heterozygous parents are carriers of the disease-causing allele, andthe probability of inheritance increases with inbreeding, mating between close relatives.dominant inheritance in whichone dominant allele is needed to show disease anddominant lethal alleles are usually eliminated from the population.0© 2012 Pearson Education, Inc.Figure 9.9AParentsOffspringSpermEggsNormalDdNormalDdDDddDDNormalDdNormal(carrier)DdNormal(carrier)ddDeaf9.9 CONNECTION: Many inherited disorders in humans are controlled by a single geneThe most common fatal genetic disease in the United States is cystic fibrosis (CF), resulting in excessive thick mucus secretions. The CF allele isrecessive andcarried by about 1 in 31 Americans.Dominant human disorders includeachondroplasia, resulting in dwarfism, andHuntington’s disease, a degenerative disorder of the nervous system.0© 2012 Pearson Education, Inc.Table 9.9New technologies offer ways to obtain genetic informationbefore conception,during pregnancy, andafter birth.Genetic testing can identify potential parents who are heterozygous carriers for certain diseases.9.10 CONNECTION: New technologies can provide insight into one’s genetic legacy0© 2012 Pearson Education, Inc.Several technologies can be used for detecting genetic conditions in a fetus.Amniocentesis extracts samples of amniotic fluid containing fetal cells and permitskaryotyping andbiochemical tests on cultured fetal cells to detect other conditions, such as Tay-Sachs disease.Chorionic villus sampling removes a sample of chorionic villus tissue from the placenta and permits similar karyotyping and biochemical tests.9.10 CONNECTION: New technologies can provide insight into one’s genetic legacy0© 2012 Pearson Education, Inc.Figure 9.10AAmniocentesisUltrasoundtransducerFetusPlacentaUterusCervixAmniotic fluidextractedCentrifugationAmniotic fluidFetal cellsCulturedcellsSeveral hoursSeveral weeksSeveral weeksBiochemicaland geneticstestsSeveral hoursSeveral hoursFetal cellsCervixUterusChorionicvilliPlacentaFetusUltrasoundtransducerTissue extractedfrom the chorionic villiChorionic Villus Sampling (CVS)KaryotypingBlood tests on the mother at 14–20 weeks of pregnancy can help identify fetuses at risk for certain birth defects.Fetal imaging enables a physician to examine a fetus directly for anatomical deformities. The most common procedure is ultrasound imaging, using sound waves to produce a picture of the fetus.Newborn screening can detect diseases that can be prevented by special care and precautions.9.10 CONNECTION: New technologies can provide insight into one’s genetic legacy0© 2012 Pearson Education, Inc.New technologies raise ethical considerations that includethe confidentiality and potential use of results of genetic testing,time and financial costs, anddetermining what, if anything, should be done as a result of the testing.9.10 CONNECTION: New technologies can provide insight into one’s genetic legacy0© 2012 Pearson Education, Inc.VARIATIONS ON MENDEL’S LAWS© 2012 Pearson Education, Inc.9.11 Incomplete dominance results in intermediate phenotypesMendel’s pea crosses always looked like one of the parental varieties, called complete dominance.For some characters, the appearance of F1 hybrids falls between the phenotypes of the two parental varieties. This is called incomplete dominance, in whichneither allele is dominant over the other andexpression of both alleles occurs.0© 2012 Pearson Education, Inc.Figure 9.11AP generationF1 generationF2 generation212121212121GametesGametesEggsSpermRedRRWhiterrPink hybridRrRRRRrrrrRRrRRrrr9.11 Incomplete dominance results in intermediate phenotypesIncomplete dominance does not support the blending hypothesis because the original parental phenotypes reappear in the F2 generation.One example of incomplete dominance in humans is hypercholesterolemia, in whichdangerously high levels of cholesterol occur in the blood andheterozygotes have intermediately high cholesterol levels. 0© 2012 Pearson Education, Inc.Figure 9.11BNormalMild diseaseSevere diseasePhenotypesCellLDLreceptorLDLHHHomozygousfor ability to makeLDL receptorshhHomozygousfor inability to makeLDL receptorsGenotypesHhHeterozygous9.12 Many genes have more than two alleles in the populationAlthough an individual can at most carry two different alleles for a particular gene, more than two alleles often exist in the wider population.Human ABO blood group phenotypes involve three alleles for a single gene.The four human blood groups, A, B, AB, and O, result from combinations of these three alleles.The A and B alleles are both expressed in heterozygous individuals, a condition known as codominance.0© 2012 Pearson Education, Inc.9.12 Many genes have more than two alleles in the populationIn codominance,neither allele is dominant over the other andexpression of both alleles is observed as a distinct phenotype in the heterozygous individual.AB blood type is an example of codominance.0© 2012 Pearson Education, Inc.Figure 9.12Blood Group(Phenotype)GenotypesCarbohydrates Presenton Red Blood CellsAntibodiesPresentin BloodABABOIAIAorIAiIBIBorIBiIAIBiiCarbohydrate ACarbohydrate BCarbohydrate AandCarbohydrate BNeitherAnti-BAnti-AAnti-BAnti-ANoneNo reactionClumping reactionOABABReaction When Blood from Groups Below Is Mixedwith Antibodies from Groups at Left9.13 A single gene may affect many phenotypic charactersPleiotropy occurs when one gene influences many characteristics.Sickle-cell disease is a human example of pleiotropy. This diseaseaffects the type of hemoglobin produced and the shape of red blood cells andcauses anemia and organ damage.Sickle-cell and nonsickle alleles are codominant.Carriers of sickle-cell disease are resistant to malaria.0© 2012 Pearson Education, Inc.Figure 9.13AFigure 9.13BAn individual homozygous for the sickle-cell alleleProduces sickle-cell (abnormal) hemoglobinThe abnormal hemoglobin crystallizes,causing red blood cells to become sickle-shapedSickled cellThe multiple effects of sickled cellsDamage to organsOther effectsKidney failureHeart failureSpleen damageBrain damage (impaired mental function, paralysis)Pain and feverJoint problemsPhysical weaknessAnemiaPneumonia and other infections9.14 A single character may be influenced by many genesMany characteristics result from polygenic inheritance, in which a single phenotypic character results from the additive effects of two or more genes.Human skin color is an example of polygenic inheritance.0© 2012 Pearson Education, Inc.Figure 9.14P generationF1 generationF2 generationEggsSpermSkin colorFraction of populationaabbcc(very light)AABBCC(very dark)AaBbCcAaBbCc816415642064664164156466418181818181818181818181818181819.15 The environment affects many charactersMany characters result from a combination of heredity and the environment. For example,skin color is affected by exposure to sunlight,susceptibility to diseases, such as cancer, has hereditary and environmental components, andidentical twins show some differences.Only genetic influences are inherited.0© 2012 Pearson Education, Inc.THE CHROMOSOMAL BASIS OF INHERITANCE© 2012 Pearson Education, Inc.9.16 Chromosome behavior accounts for Mendel’s lawsThe chromosome theory of inheritance states that genes occupy specific loci (positions) on chromosomes andchromosomes undergo segregation and independent assortment during meiosis.0© 2012 Pearson Education, Inc.9.16 Chromosome behavior accounts for Mendel’s lawsMendel’s laws correlate with chromosome separation in meiosis.The law of segregation depends on separation of homologous chromosomes in anaphase I.The law of independent assortment depends on alternative orientations of chromosomes in metaphase I. 0© 2012 Pearson Education, Inc.Figure 9.16_s1F1 generationAll yellow round seeds(RrYy)Meta-phase Iof meiosisYyRrrrRRYYyyFigure 9.16_s2F1 generationAll yellow round seeds(RrYy)Meta-phase Iof meiosisAnaphase IMetaphase IIRyrYYRryYYyyRRrrrrrRRRYYYyyyFigure 9.16_s3F1 generation41414141All yellow round seeds(RrYy)Meta-phase Iof meiosisAnaphase IMetaphase IIFertilizationGametesF2 generation9:3:3:1RYryrYRyRRRyyyrrrYYYYYYRRRrrryyyYYyyRRrrrrrRRRYYYyyyFigure 9.16_4SpermEggsYellowroundGreenroundYellowwrinkledGreenwrinkledRYRYrYrYRyRyryryRRYYRrYYRRYyRrYyRrYYrrYYRrYyrrYyRRYyRrYyRRyyRryyRrYyrrYyRryyrryy41169163163161414141414141419.17 SCIENTIFIC DISCOVERY: Genes on the same chromosome tend to be inherited togetherBateson and Punnett studied plants that did not show a 9:3:3:1 ratio in the F2 generation. What they found was an example of linked genes, whichare located close together on the same chromosome andtend to be inherited together.0© 2012 Pearson Education, Inc.Figure 9.17_1The ExperimentPurple flowerLong pollenPpLlPpLlPhenotypesObservedoffspringPrediction(9:3:3:1)Purple longPurple roundRed longRed round284212155215717124Figure 9.17_2The Explanation: Linked GenesParentaldiploid cellPpLlMeiosisP LP Lp lp lMostgametesFertilizationSpermMostoffspringEggs3 purple long : 1 red roundNot accounted for: purple round and red longP LP LP LP LPLPLp lp lp lp lplpl9.18 SCIENTIFIC DISCOVERY: Crossing over produces new combinations of allelesCrossing over between homologous chromosomes produces new combinations of alleles in gametes.Linked alleles can be separated by crossing over, forming recombinant gametes.The percentage of recombinants is the recombination frequency.0© 2012 Pearson Education, Inc.Figure 9.18AP LTetrad(pair ofhomologouschromosomes)p lp lp Lp LP lCrossing overParental gametesRecombinant gametesFigure 9.18C_1The ExperimentFemaleMaleggllGgLlBlack body,vestigial wingsGray body,long wings(wild type)Offspring:Gray longBlack vestigialGray vestigialBlack longRecombinantphenotypesParentalphenotypesRecombination frequency  0.17 or 17% 391 recombinants2,300 total offspring965944206185Figure 9.18C_2OffspringParentalRecombinantEggsSpermCrossing overG Lg lg lg lg lg lG lg LG Lg lG lg Lg lg lg lg lThe ExplanationGgLlFemaleggllMaleG L9.19 Geneticists use crossover data to map genesWhen examining recombinant frequency, Morgan and his students found that the greater the distance between two genes on a chromosome, the more points there are between them where crossing over can occur.Recombination frequencies can thus be used to map the relative position of genes on chromosomes.0© 2012 Pearson Education, Inc.Figure 9.19ASection of chromosome carrying linked genesRecombinationfrequencies17%9%9.5%gclFigure 9.19BMutant phenotypesShortaristaeBlackbody(g)Cinnabareyes(c)Vestigialwings(l)Brown eyesRed eyesNormalwings(L)Redeyes(C)Graybody(G)Long aristae(appendageson head)Wild-type phenotypesSEX CHROMOSOMES AND SEX-LINKED GENES© 2012 Pearson Education, Inc.9.20 Chromosomes determine sex in many speciesMany animals have a pair of sex chromosomes,designated X and Y, that determine an individual’s sex.In mammals,males have XY sex chromosomes,females have XX sex chromosomes,the Y chromosome has genes for the development of testes, andan absence of the Y allows ovaries to develop. 0© 2012 Pearson Education, Inc.Figure 9.20AXYFigure 9.20BParents(diploid)Gametes(haploid)Offspring(diploid)FemaleFemaleMaleMaleEggSperm44XY44XX22X22Y22X44XX44XYFigure 9.21AFigure 9.21A_1Figure 9.21A_2Figure 9.21BMaleFemaleSpermEggsR  red-eye alleler  white-eye alleleXRXrXrYXRXRXRXrXRYYFigure 9.21CR  red-eye alleler  white-eye alleleMaleFemaleSpermEggsXRxRXRYXRXrYXrXrYXRYXRXRXrXRFigure 9.21DR  red-eye alleler  white-eye alleleMaleFemaleSpermEggsXrYXRXrXrXrXrXRXrYXrYXRYXRXr9.22 CONNECTION: Human sex-linked disorders affect mostly malesMost sex-linked human disorders aredue to recessive alleles andseen mostly in males.A male receiving a single X-linked recessive allele from his mother will have the disorder.A female must receive the allele from both parents to be affected.0© 2012 Pearson Education, Inc.9.22 CONNECTION: Human sex-linked disorders affect mostly malesRecessive and sex-linked human disorders includehemophilia, characterized by excessive bleeding because hemophiliacs lack one or more of the proteins required for blood clotting,red-green color blindness, a malfunction of light-sensitive cells in the eyes, andDuchenne muscular dystrophy, a condition characterized by a progressive weakening of the muscles and loss of coordination.0© 2012 Pearson Education, Inc.Figure 9.22FemaleMaleHemophiliaCarrierNormalAlexisAlexandraCzarNicholas IIof RussiaQueenVictoriaAliceLouisAlbert9.23 EVOLUTION CONNECTION: The Y chromosome provides clues about human male evolutionThe Y chromosome provides clues about human male evolution becauseY chromosomes are passed intact from father to son andmutations in Y chromosomes can reveal data about recent shared ancestry.0© 2012 Pearson Education, Inc.