Mosaicism

Since humans consist of more than ten trillion cells, it is not surprising that mutations occur in the genes in some of these cells, rendering the individual a mosaic. In some cases such changes have limited impact and are found in only a few cells. In other cases they may lead to cancer or disease.

We are all likely to have some cells in our body that have acquired mutations, and therefore everyone may be considered a mosaic at some level. Mosaicism can create differences among a person's cells. It can also result in differences between "identical" twins.

Most females are mosaics, due to X chromosome inactivation, though their mosaicism does not necessarily involve any disease gene. Chromosomal and mitochondrial mosaicism are also observed frequently.