A mitochondrial model for premature ageing of somatically cloned mammals

Cloned sheep have recently been discovered to have an unexpectedly advanced biological age. We propose that the explanation is a simple consequence of inheritance of acquired, free radical-induced cellular damage with somatic mitochondria that contribute to the mitochondrial population of cloned cel ls but not to zygotes produced by fertilization in normal sexual reproducti on. Each increment of ageing in cloning experiments is therefore predicted to be maternally inherited. The hypothesis suggests practical ways of decre asing the effect. The hypothesis is itself a prediction of the recent propo sal that mitochondria of the female germ line function primarily as genetic templates.