ADAPTIVE MUTATION - A GENERAL PHENOMENON OR SPECIAL CASE

A recent article by Galitski and Roth((1)) characterizes adaptive reve rsion of chromosomal lac(-) mutations in Salmonella typhimurium LT2. U sing a classical genetic approach they show that adaptive reversion, a s characterized by the appearance of late revertant colonies, is an ex ception rather than a general phenomenon for reversion of nonsense, mi ssense, frameshift and insertion mutations. For certain mutations, how ever, the number of late revertants exceeds the predicted number. Thes e excess revertants suggest that adaptive mutability is applicable to chromosomal genes as well as to genetic changes involving F plasmids a nd lysogenic phages.