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1、03基因突变GeneMutationGeneMutationChangeingenescausedbychangeinstructureoftheDNA.Base(s)inDNAis(are)changedtoother(s),orabase(s)is(are)addedorremoved.Rearrangementsofthechromosomesoccurandarealsoconsidered.Mutationsareheritablechangesingeneticmaterial.1.Mutagen
2、sorMutagenicAgentsThesearesubstances,conditionsandformsthatsignificantlyincreasethefrequencyofmutations.Mutationscanoccurataspontaneousrate,orafargreaterratewhenthereisexposuretomutagenicagents.Exposuretotoohighalevelofmutagenscanthreatenthesurvivalofaspeci
3、es;e.g.,frogspeciesinthestatesofWashingtonandOregonarefacingextinction.Thisappearstobecausedbyreducedatmosphericozone,andtheresultingincreasedlevelofultravioletradiation.AformsofenergyExamplesofaformsofenergyareultravioletlight,x-rays,cosmicenergy,gammaradi
4、ation,alphaparticles,betaparticlesandneutrons.Ultraviolet(UV)lightUVlighthasshorterwavelengthsthanvisiblelight.Thoughthesewavesareinvisibletothehumaneye,someinsects,likebumblebees,canseethem!Scientistshavedividedtheultravioletpartofthespectrumintothreeregio
5、ns:thenearultraviolet,thefarultraviolet,andtheextremeultraviolet.Thethreeregionsaredistinguishedbyhowenergetictheultravioletradiationis,andbythe"wavelength"oftheultravioletlight,whichisrelatedtoenergy.Thenearultraviolet,abbreviatedNUV,isthelightclosesttoopt
6、icalorvisiblelight.Theextremeultraviolet,abbreviatedEUV,istheultravioletlightclosesttoX-rays,andisthemostenergeticofthethreetypes.Thefarultraviolet,abbreviatedFUV,liesbetweenthenearandextremeultravioletregions.Itistheleastexploredofthethreeregions.Ultraviol
7、etRadiationcausespyrimidinedimers.ThesecanblockDNAreplication.Also,dimersinterferewithbasepairingbetweenthetwoDNApolymeres.U.V.lightalsogeneratesfree-radicals,whichcreateotherkindsofgeneticdamage.GammaandX-RaysThesecanactdirectlyonDNA;however,mostdamageisca
8、usedindirectlywhenmoleculesaroundtheDNAsuchaswater,areionized,creatingfree-radicals,substanceswithunpairedelectrons.Mostoften,theresultissingleordoublestrandedbreaksintheDNAmolecules.Thesebreaksarehard
