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A somatic mutation occurs in a body-cell lineage outside the germline mutation route. Its descendant biological cells can inherit it through DNA replication, even though it is not transmitted through gametes. Thus heritability within a cell lineage differs from inheritance between sexually reproducing organisms.

Silencing of much of one X chromosome in a cell lineage. In a heterozygous retina it can create a mosaic of cells expressing different X-linked opsin variants. That mosaic provides potential spectral diversity but does not by itself establish tetrachromacy.