In an epigenetic mosaic (in contrast to a genomic mosaic), all cells of the mosaic have the same genome. Due to early epigenetic influences of control genes, which start during embryogenesis, two functionally different cell clones are formed.
These functional mosaics are heritable. Such a mosaic can affect both the X chromosomes and the autosomes. All epigenetic mosaics are thought to be caused by the activity of transposable elements, also called retrotransposons.