From the fertilization of an egg until the death of an individual, somatic cells can accumulate genetic changes, such that cells from different tissues or even within the same tissue differ genetically. The presence of multiple cell clones with distinct genotypes in the same individual is referred to as 'somatic mosaicism'. Many endogenous factors such as mobile elements, DNA polymerase slippage, DNA double-strand break, inefficient DNA repair, unbalanced chromosomal segregation and some exogenous factors such as nicotine and UV exposure can contribute to the generation of somatic mutations, thereby leading to somatic mosaicism. Such changes can potentially affect the epigenetic patterns and levels of gene expression, and ultimately the phenotypes of cells. Although recent studies suggest that somatic mosaicism is widespread during normal development and aging, its implications for heightened disease risks are incompletely understood. Here, I discuss the origins, prevalence and implications of somatic mosaicism in healthy human tissues.
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