Human Molecular Genetics_ch09

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1、Chapter9OrganizationoftheHumanGenome9KEYCONCEPTS•Thehumangenomeissubdividedintoalargenucleargenomewithmorethan26,000genes,andaverysmallcircularmitochondrialgenomewithonly37genes.Thenucleargenomeisdistributedbetween24linearDNAmolecules,oneforeachofthe24differenttyp

2、esofhumanchromosome.•Humangenesareusuallynotdiscreteentities:theirtranscriptsfrequentlyoverlapthosefromothergenes,sometimesonbothstrands.•Duplicationofsinglegenes,subchromosomalregions,orwholegenomeshasgivenrisetofamiliesofrelatedgenes.•Genesaretraditionallyviewed

3、asencodingRNAfortheeventualsynthesisofproteins,butmanythousandsofRNAgenesmakefunctionalnoncodingRNAsthatcanbeinvolvedindiversefunctions.•NoncodingRNAsoftenregulatetheexpressionofspecifictargetgenesbybasepairingwiththeirRNAtranscripts.•Somecopiesofafunctionalgenecom

4、etoacquiremutationsthatpreventtheirexpression.ThesepseudogenesoriginateeitherbycopyinggenomicDNAorbycopyingaprocessedRNAtranscriptintoacDNAsequencethatreintegratesintothegenome(retrotransposition).•Occasionally,genecopiesthatoriginatebyretrotranspositionretainthei

5、rfunctionbecauseofselectionpressure.Theseareknownasretrogenes.•Transposonsaresequencesthatmovefromonegenomiclocationtoanotherbyacut-and-pasteorcopy-and-pastemechanism.RetrotransposonsmakeacDNAcopyofanRNAtranscriptthatthenintegratesintoanewgenomiclocation.•Verylarg

6、earraysofhigh-copy-numbertandemrepeats,knownassatelliteDNA,areassociatedwithhighlycondensed,transcriptionallyinactiveheterochromatininhumanchromosomes.256Chapter9:OrganizationoftheHumanGenome1.1%~4%Figure9.1Sequenceconservationandsequenceclassesinthehumannuclearan

7、dmitochondrialgenomes.Togetan<2%ideaofthevastdifferenceinscalebetweenthenuclear(left)andmitochondrial(right)genomes,thetinyreddotinthecenterrepresentstheequivalentof~44%~32%25mitochondrialDNA(mtDNA)genomeson~45%thesamescaleasthesinglenucleargenome~66%ontheleft.Note

8、alsotheprofounddifferencebetweenthetwogenomesinthefractionsofhighlyconservedDNAandalsointhefractionofhighlyrepetitivenoncodingDNA.~6.5%mitochondrialgenom