Mapping and Sequencing the Genome 



To determine the order of billions of pairs of raw DNA sequence, first the human 

 genome must he broken down into genes or other fragments small enough to be 

 propagated by cloning techniques and characterized for identification. Next, these 

 chromosomal fragments will be ordered — mapped — to correspond to their respective 

 locations on the chromosomes. Finally, automated techniques will be utilized to 

 determine the base sequence of the ordered fragments — the ultimate goal of the Human 

 Genome Project. 



Molecular Techniques Used in the Human Genome Project 



Improvements in mapping and sequencing techniques are a major focus of the genome 

 project. The efforts will include developing automated probe and mapping methods, as 

 well as optimizing techniques to extract the maximum useful information from maps 

 and sequences. Some of the techniques currently being employed are described below. 



Using Restriction Enzymes 



Isolated from various bacteria, restriction enzymes serve as microscopic scalpels that 

 recognize short sequences of DNA and cut the DNA molecules at those specific 

 recognition sites (Fig. 5). 



Fig. 5. Typical restriction enzyme 

 cutting sites. The recognition site 

 has a twofold symmetry around a 

 point (the dashed line). The cutting 

 sites (arrows) are on both strands of 

 the double helix (above and below 

 the solid line) and. when cut, 

 generate smaller, linear fragments 

 of DNA. 



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