新编英语教程 4 Unit 13 拓展知识

Furtherdevelopment,1.definitionofcloningCloning,creatingacopyoflivingmatter,suchasacellororganism.Thecopiesproducedthroughcloninghaveidenticalgeneticmakeupandareknownasclones.Manyorganismsinnaturereproducebycloning.Scientistsusecloningtechniquesinthelaboratorytocreatecopiesofcellsororganismswithvaluabletraits.Theirworkaimstofindpracticalapplicationsforcloningthatwillproduceadvancesinmedicine,biologicalresearch,andindustry.,2.HOWSCIENTISTSCLONECELLS,A.BlastomereSeparationInblastomereseparation,scientistsfertilizeaneggcellwithaspermcellinalaboratorydish.Theresultingembryoisallowedtodivideuntilitformsamassofaboutfourcells.Scientistsremovetheoutercoatingoftheembryoandplaceitinaspecialsolutionthatcausestheindividualcellsoftheembryo,knownasblastomeres,toseparate.Scientiststhenputeachblastomereinculture,whereitformsanembryocontainingthesamegeneticmakeupastheoriginalembryo.Eachnewembryocanthenbeimplantedintotheuterusofasurrogatemothertodevelopduringanormalpregnancy.,B.BlastocystDivisionInblastocystdivision,scientistsallowafertilizedeggtodivideuntilitformsamassofabout32to150cells,knownasablastocyst.Scientiststhensplittheblastocystintwoandimplantthetwohalvesintotheuterusofasurrogatemother.Thetwohalvesdevelopasidenticaltwins.,C.SomaticCellNuclearTransferWhileblastomereseparationandblastocystdivisionproduceanimalscontainingthegeneticmaterialfrombothamotherandfather,somaticcellnucleartransferproducesananimalcarryingthegeneticmaterialofonlyoneparent.Inthistechnique,scientiststransferthegeneticmaterialfromadonorssomaticcell(anybodycellotherthananeggorspermcell)toanenucleatedeggcellthatis,aneggcellwithitsnucleus,andthusitsgeneticmaterial,removed.Theresultingclonedcellcontainsthegeneticmaterialofthedonorssomaticcell.,GeneticEngineering,Geneticengineeringenablesscientiststoproduceclonesofcellsororganismsthatcontainthesamegenes.1.Scientistsuserestrictionenzymestoisolateasegmentofdeoxyribonucleicacid(DNA)thatcontainsageneofinterestforexample,thegeneregulatinginsulinproduction.2.AplasmidremovedfromabacteriumandtreatedwiththesamerestrictionenzymebindswiththeDNAfragmenttoformahybridplasma.3.Thehybridplasmidisre-insertedbackintothebacterium,whereitreplicatesaspartofthecellsDNA.4.Alargenumberofidenticaldaughtercells(clones)canbeculturedandtheirgeneproductsextractedforhumanuse.,FirstClonedCat,Theworldsfirstcatclone,namedCC,forcarboncopyorcourtesycopy,wasproducedbyscientistsatTexasA&MUniversityinCollegeStation.BornDecember22,2001,thekittenwasclonedusingamethodcallednucleartransfer,inwhichnucleifromcellsofanadultanimalareinsertedintoeggcellswithnucleiremoved.Theembryosthatresultarethenimplantedintotheuterusofasurrogatemother,wheretheydevelopinanormalpregnancy.,IdenticalCalves,Twoofeightcalvesclonedfromcellsobtainedfromoneadultcows