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1、TheInfluenceofHeredity onDevelopmentHeredityandGeneticsHeredityOne’snaturebasedonbiologicaltransmissionoftraitsandcharacteristicsGeneticsFieldwithinthescienceofbiologythatstudiesheredityGeneticsInfluenceourPhysicaltraitsBehavioraltraitsPsychologicalproblemsWhatAreC
2、hromosomesandGenes?ChromosomesFoundincells23pairsGenesSegmentsofDNAwithinchromosomesRegulatedevelopmentoftraitsTransmittedbysinglegeneormaybepolygenic20,000to25,000genesineverycellDoubleHelixofDNAFigure2.1TwoTypesofCellDivisionMitosisCelldivisionbywhichgrowthoccurs
3、StrandsofDNAbreakapart,duplicateandarerebuiltResultisidenticalcopiesofDNAstrandMutationscandevelopthroughoutourlivesTwoTypesofCellDivisionMeiosisCelldivisionbywhichspermandovaareproduced23chromosomepairsdivideResultisanewcellwithonly23chromosomes22pairsareautosomes
4、23rdpairaresexchromosomesTwoTypesofCellDivisionMeiosisCrossingOverThe23PairsofHumanChromosomesFigure2.3HowAreTwinsFormed?MonozygoticTwins(MZ)DerivedfromasinglezygotethathassplitintwoIdenticaltwinsDizygoticTwins(DZ)DerivedfromtwozygotesProbabilityoftwinsincreasesMat
5、ernalageUseoffertilitydrugsHowDoGenesDetermineTraits?TraitsaredeterminedbypairsofgenesEachmemberofpairisanalleleHomozygousBothallelesforatraitarethesameHeterozygousAllelesforatraitaredifferentMendel’sLawsofHeredityAveragingEffectsofbothallelesareshownLawofDominance
6、DominantallelepairedwithrecessivealleleDominantalleleappearsinoffspringTransmissionofDominantandRecessiveTraitsFigure2.4TransmissionofDominantandRecessiveTraitsDominantandRecessiveTraitsCarriersPersonwhohasonedominantandonerecessivegeneChromosomalorgeneticabnormali
7、tiesOccurinautosomesorsexchromosomesMaybecausedbyasinglegeneorcombinationsChromosomalAbnormalities:DownSyndromeCause:extrachromosomeon21stpairProbabilityincreaseswithincreasedageofparentCharacteristicsofchildrenFacialfeaturesCognitiveandphysicaldeficienciesDownSynd
8、romeFigure2.5ChromosomalAbnormalities:Sex-LinkedMostareinfertileMalewithextrasexchromosomeXYY-extraYchromosomeXXY-KlinefeltersyndromeFemalewithab
