genetic information. The two DNA strands are related by the following rules for 

 matching — pairing — the four bases: 



• A on one strand is always matched by T on the other to form an A-T base pair. 



• G on one strand is always matched by C on the other to form a G-C base pair. 



Adherence to these rules ensures that a duplicate information set is available to correct 

 errors and thus minimize the mutation rate. 



When a cell divides, its DNA divides too. Using the rules for forming base pairs, each 

 strand directs the synthesis of a complementary new strand. Each daughter cell receives 

 one old and one new DNA strand (Figs. 1 and 3). 



Fig. 3. Replication of DNA. 



Complementary DNA strands 

 separate; each strand then 

 becomes the template for 

 synthesis of a new strand. 



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