Accomplishments 



Restriction maps of large regions of chromosome 21 completed. By using (a) single- 

 copy probes with i<nown regional locations to assign fragments and (b) partial digests, 

 chromosome-specific Not 1 linking probes, and polymorphism among cell lines to 

 assign neighboring bands, LBL researchers have identified about 40 Mb of DNA from 

 chromosome 21 and linked Not I fragments in several regions of the c/ ami; these 

 fragments include a continuous section that starts at the telomere and extends for 

 8.5 Mb. 



Physical Mapping 



A pulsed-fleld gel electrophoresis test bed. The basic DNA separation technique of modern molecular biology is gel 

 electrophoresis — in particular, pulsed-field gel (PFG) electrophoresis. In the PFG lest bed shown here (left), conditions 

 at any point in the gel can be monitored by a probe mounted on a computer-controlled platform (right). Parameters such 

 as current, gel temperature, and pH can now be monitored to optimize conditions and to assure reproducibility among 

 different PFG sessions. The test bed allows active computer control of electrode potentials, as well as the capability for 

 programming complex pulse cycles. The results of continuing studies with this and other test beds will be increased 

 resolution and shorter separation times, especially for DNA fragments of more than 5 Mbp. (Photographs provided by 

 the Human Genome Center, Lawrence Berkeley Laboratory.) 



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