for 13 years, the murder of bio-tech research scientist helena greenwood went unsolved. the medical examiner found what looked to be blood under one of her fingernails. at the time, it was far too small for dna analysis. by 1998, however, work that gen-probe and scientists like helena greenwood had been working on led to new developments in dna testing. one of the most important was polymerase chain reaction or pcr which enabled scientists to copy minute dna samples until they were large enough to test. >> polymerase chain reaction allows you to make dramatically