 In transgenerational epigenetic transmission, alternative phenotypes can persist for several, possibly many, generations, though their persistence may be more limited than that of genetic changes. They may thus have evolutionary effects in addition to the role played by cellular epigenetic inheritance in the development of multi-cellular organisms that was noted above. Generally, epigenetic inheritance piggybacks on general developmental and physiological mechanisms of cells, and is a by product of other physiological functions, not the result of an independent copying system that is content neutral; DNA methylation is a notable exception. Epigenetic inheritance typically is holistic rather than modular in its storage and transmission (i.e., it is not comprised of units of information that can be changed independently of one another), and supports a limited repertoire of hereditary variants (e.g., the steady-states of a metabolic cycle). However, one cell may include many instances of independent self-sustaining metabolic cycles and structurally transmitted cellular components, for example, increasing the repertoire of cellular variations that can be inherited via these forms of inheritance. Typically, EISs (with some exceptions, such as DNA methylation) cannot transmit unexpressed (latent) information, although the transmission of partial factors or marks, which are not sufficient for expression, may be reliably sufficient when additional developmental factors are added.