The Muller's Ratchet and Aging.

Aging entails an irreversible deceleration of physiological processes, altered metabolic activities, and a decline of the integrity of tissues, organs, and organ systems. The accumulation of alterations in the genetic and epigenetic spaces has been proposed as an explanation for aging. They result, at least in part, from DNA replication and chromosome segregation errors due to cell division during development, growth, renewal, and repair. Such deleterious alterations, including epigenetic drift, irreversibly accumulate in a stepwise, ratchet-like manner and reduce cellular fitness, similar to the process known as Muller's ratchet. Here, we revisit the Muller's ratchet principle applied to the aging of somatic cell populations and discuss the implications for understanding the origins of senescence, frailty, and morbidity.