IS MITOCHONDRIAL-DNA A STRICTLY NEUTRAL MARKER

Variation and change in mitochondrial DNA (mtDNA) is often assumed to conform to a constant mutation rate equilibrium neutral model of molec ular evolution. Recent evidence, however, indicates that the assumptio ns underlying this model are frequently violated. The mitochondrial ge nome may be subject to the same suite of forces known to be acting in the nuclear genome, including hitchhiking and selection, as well as fo rces that do not affect nuclear variation. Wherever possible, evolutio nary studies involving mtDNA should incorporate statistical tests to i nvestigate the forces shaping sequence variation and evolution.