 Thus, a knowledge of mutation bias can be used to design more evolution-resistant therapies.When mutation bias is invoked as a possible cause of some pattern of asymmetry in evolution, the alternative hypotheses may include selection, biased gene conversion, and demographic factors.In the past, due to the technical difficulty of detecting rare mutations, most attempts to characterize the mutation spectrum were based on reporter gene systems, or based on patterns of presumptively neutral change in pseudogenes.