Appendix A: 

 Primer on Molecular 

 Genetics 



End Games: Completing the Maps and Determining 

 the Sequences 



Starting maps and sequences is relatively easy; finishing them is very difficuU. New 

 methods are needed to expedite this end game. 



Chromosome Walking with Primers 



An approach being used to finish sequences is chromosome walking with primers 

 (Fig. 14). In this technique, the walk begins with a primer at a known site and proceeds 

 in a linear fashion — one step at a time — while adjacent regions that were previously 

 unknown are being identified and sequenced. The larger region then serves as the new 

 primer. All primers are synthesized chemically. The difficulty with this technique is the 

 number of syntheses required for a large project. 



Fig. 14. Chromosome walking. 



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