GENETIC CONFLICTS

Self-promoting elements (also called ultraselfish genes, selfish genes , or selfish genetic elements) are vertically transmitted genetic enti ties that manipulate their ''host'' so as to promote their own spread, usually at a cost to other genes within the genome. Examples of such elements include meiotic drive genes and cytoplasmic sex ratio distort ers. The spread of a self-promoting element creates the context for th e spread of a suppressor acting within the same genome. We may thus sa y that a genetic conflict exists between different components of the s ame genome. Here we investigate the properties of such conflicts. Firs t we consider the potential diversity of genomic conflicts and show th at every genetic system has potential conflicts. This is followed by a nalysis of the logic of conflicts. Just as Evolutionarily Stable Strat egy (ESS) terminology provides a short cut for discussion of much in b ehavioral ecology, so the language of modifier analysis provides a use ful terminology on which to base discussions of conflicts. After defin ing genetic conflict, we provide a general analysis of the conflicting parties, and note a distinction between competing and conflicting gen es. We then provide a taxonomy of possible short- and long-term outcom es of conflicts, noting that potential conflict in an unconstrained sy stem can never be removed, and that the course of evolution owing to c onflict is often unpredictable. The latter is most particularly true f or strong conflicts in which suppressors may take surprising forms. Th e possibility of extended conflicts in the form of ''arms races'' betw een element and suppressor is illustrated. The peculiar redundancy of these systems is one possible trace of conflict, and others are discus sed. That homologous conflicts may find highly different expression is discussed by referring to the mechanistic differences that are though t to underlie the action of the two best-described meiotic drive genes , and by the multiplicity of forms of cytoplasmic sex ratio distorters . The theoretical analysis establishes a logical basis for thinking ab out conflicts, but fails to establish the importance of conflict in ev olution. We illustrate this contentious issue through consideration of some phenomena for whose evolution conflict has been proposed as an i mportant force: the evolution of sex, sex determination, species, reco mbination, and uniparental inheritance of cytoplasmic genes. In genera l, it is proposed that conflict may be a central force in the evolutio n of genetic systems. We conclude that an analysis of conflict and its general importance in evolution is greatly aided by application of th e concept of genetic power. We consider the possible components of gen etic power and ask whether and how power evolves.