Last reviewed 01/2018

A mosaic organism is composed of two or more genetically different cell lines which are all derived from a single zygote.

The mosaicism derives from nondisjunction or chromosome lag during one of the mitoses during early embryogenesis.

The most common form of genetic mosaicism is disomy/trisomy mosaics for a particular chromosome; about 1% of Down's syndrome patients are disomy/trisomy mosaics for chromosome 21.

Polyploidy mosaics are occasionally found e.g. diploid/triploid mosaics.

Usually mosaics suffer a mild form of the disease associated with the aneuploid genome.