The most obvious is intheir role in increasing our understandingof biology. The fi rst genome sequencesto be revealed were those of viruses (RNAbacteriophage MS2 and DNA bacteriophageX174). The basic technology of geneticmanipulation was developed from studieswith bacterial viruses, and viral elementsare still widely used in such work (describedin more detail in Chapter 9). And thereverse fl ow of genetic information (RNA toDNA) was discovered from work with theRetroviridae.CHAPTER 7Benefi cial Use ofViruses