Trasposable Elements: P Elements

In 1938 Marcus Rhodes provided the first genetic description of an unstable mutation, an allele of a gene required for the production of pigment in maize. This instability resulted in a variegated phenotype. Variegation describes irregular patterns of pigmentation and reflects changes in the expression of genes that control pigment production. Rhodes defined two genes required for this instability: the unstable allele defined one gene, and a dominant mutation called Dotted that controlled this instability mapped to a separate locus, defining a second gene. In the 1940s and 1950s Barbara McClintock showed that this type of instability was caused by genetic elements that transposed from one locus to another. It was not until the description of transposable elements in bacteria two decades later that McClintock's work was truly appreciated. McClintock won the Nobel Prize for her work on transposable elements in 1983. Drosophila P elements were also identified by genetic criteria. The ability of geneticists to regulate the movement of P elements has led to the use of these elements as powerful genetic tools.