Selfish genetic elements.

Complex genetic systems appear to be inherently vulnerable to subversion by 'selfish' genetic elements, which gain a transmission advantage relative to the rest of the genome and are often detrimental to the organism. Such elements appear to have evolved many times, and show diverse origins and mechanisms for gaining a transmission advantage. The purpose of this report is to indicate how widespread such selfish genetic elements are, and to review the main evolutionary and population genetic questions relating to them.