新编英语教程 4 Unit 13 拓展知识

Furtherdevelopment•1.definitionofcloning•Cloning,creatingacopyoflivingmatter,suchasacellororganism.Thecopiesproducedthroughcloninghaveidenticalgeneticmakeupandareknownasclones.Manyorganismsinnaturereproducebycloning.Scientistsusecloningtechniquesinthelaboratorytocreatecopiesofcellsororganismswithvaluabletraits.Theirworkaimstofindpracticalapplicationsforcloningthatwillproduceadvancesinmedicine,biologicalresearch,andindustry.2.HOWSCIENTISTSCLONECELLS•A.BlastomereSeparation•Inblastomereseparation,scientistsfertilizeaneggcellwithaspermcellinalaboratorydish.Theresultingembryoisallowedtodivideuntilitformsamassofaboutfourcells.Scientistsremovetheoutercoatingoftheembryoandplaceitinaspecialsolutionthatcausestheindividualcellsoftheembryo,knownasblastomeres,toseparate.Scientiststhenputeachblastomereinculture,whereitformsanembryocontainingthesamegeneticmakeupastheoriginalembryo.Eachnewembryocanthenbeimplantedintotheuterusofasurrogatemothertodevelopduringanormalpregnancy.•B.BlastocystDivision•Inblastocystdivision,scientistsallowafertilizedeggtodivideuntilitformsamassofabout32to150cells,knownasablastocyst.Scientiststhensplittheblastocystintwoandimplantthetwohalvesintotheuterusofasurrogatemother.Thetwohalvesdevelopasidenticaltwins.•C.SomaticCellNuclearTransfer•Whileblastomereseparationandblastocystdivisionproduceanimalscontainingthegeneticmaterialfrombothamotherandfather,somaticcellnucleartransferproducesananimalcarryingthegeneticmaterialofonlyoneparent.Inthistechnique,scientiststransferthegeneticmaterialfromadonor’ssomaticcell(anybodycellotherthananeggorspermcell)toanenucleatedeggcell—thatis,aneggcellwithitsnucleus,andthusitsgeneticmaterial,removed.Theresultingclonedcellcontainsthegeneticmaterialofthedonor’ssomaticcell.GeneticEngineering•Geneticengineeringenablesscientiststoproduceclonesofcellsororganismsthatcontainthesamegenes.1.Scientistsuserestrictionenzymestoisolateasegmentofdeoxyribonucleicacid(DNA)thatcontainsageneofinterest—forexample,thegeneregulatinginsulinproduction.2.AplasmidremovedfromabacteriumandtreatedwiththesamerestrictionenzymebindswiththeDNAfragmenttoformahybridplasma.3.Thehybridplasmidisre-insertedbackintothebacterium,whereitreplicatesaspartofthecell’sDNA.4.Alargenumberofidenticaldaughtercells(clones)canbeculturedandtheirgeneproductsextractedforhumanuse.FirstClonedCat•Theworld'sfirstcatclone,namedCC,forcarboncopyorcourtesycopy,wasproducedbyscientistsatTexasA&MUniversityinCollegeStation.BornDecember22,2001,thekittenwasclonedusingamethodcallednucleartransfer,inwhichnucleifromcellsofanadultanimalareinsertedintoeggcellswithnucleiremoved.Theembryosthatresultarethenimplantedintotheuterusofasurrogatemother,wheretheydevelopinanormalpregnancy.IdenticalCalves•TwoofeightcalvesclonedfromcellsobtainedfromoneadultcowstandinafieldinIshikawa,Japan.ThecalveswereclonedbyresearchersatKinkiUniversityinNara,Japan.Theresultsofthecloningexperimentwerepublishedin1998.