Single Chromosome Dissection 



Another approach to finishing maps is to utilize single-chromosome dissection by 

 physical methods (Fig. 15). This method isolates DNA pieces from the regions that are 

 not yet mapped or sequenced and then applies the previously described mapping 

 methods to those pieces. 



Locating Specific Genes 



The current human genetic map has about 1000 markers, or 1 marker spaced every 3 

 million base pairs. About 100 genes will lie between each pair of markers. In some 

 regions of particular interest, genetic maps have been made that are five to ten times 

 more detailed. By combining genetic and physical map infomiation for a region, the 

 stage is set for locating new genes (Fig. 16). The genetic map of these markers basically 



unibld, cut 





extend 



DNA chain 



tether 



tether 



chromosome ifr molecule 



Fig. 15. Chromosome or single- 

 molecule strategies. 



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