?url_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Adc&rft.title=Gene+targeting+studies%3A+New+methods%2C+old+problems&rft.creator=Crusio%2C+Wim+E.&rft.subject=Behavioral+Neuroscience&rft.description=Techniques+to+create+transgenic+organisms+or+animals+with+targeted+mutations+('knock-out'+mutants)+have+become+increasingly+important+tools+in+the+neurosciences+over+the+last+few+years.+As+always%2C+new+techniques%2C+besides+providing+new+tools+to+investigate+problems+or+to+test+hypotheses%2C+also+give+rise+to+unforeseen+difficulties+and+it+takes+some+time+for+researchers+to+become+aware+of+this.+Gene+targeting+techniques+provide+no+exception+and+Gerlai's1+alert+is+very+timely+indeed.+The+complications+described+by+Gerlai+are%2C+not+very+surprisingly%2C+strongly+reminiscent+of+those+encountered+in+the+study+of+spontaneous+mutations+in+the+mouse.+In+that+field+congenic+strains+have+been+used+since+many+years2.+Congenic+strains+are+obtained+by+repeatedly+backcrossing+a+mutant+to+an+inbred+strain.+If+we+now+consider+the+possible+complications+that+may+be+encountered+with+this+approach+we+may%2C+in+fact%2C+distinguish+two+rather+different+types+of+'background'+effects.+As+I+will+show+in+the+following%2C+the+distinction+between+the+two+is+crucial.&rft.date=1996&rft.type=Journal+(Paginated)&rft.type=PeerReviewed&rft.format=text%2Fhtml&rft.identifier=http%3A%2F%2Fcogprints.org%2F36%2F1%2Ftins.htm&rft.identifier=++Crusio%2C+Wim+E.++(1996)+Gene+targeting+studies%3A+New+methods%2C+old+problems.++%5BJournal+(Paginated)%5D+++++&rft.relation=http%3A%2F%2Fcogprints.org%2F36%2F