The human body is a mosaic of different genomes

The human body is a complex mosaic made up of clusters of cells with different genomes — and many of these clusters bear mutations that could contribute to cancer, according to a sweeping survey of 29 different types of tissue. Tissue mosaics arise as cells accumulate mutations — from DNA errors that creep in during cell division, or because of exposure to environmental factors such as ultraviolet light or cigarette smoke. But he says that his team was initially surprised to find that some of the mutations in their results — which are associated with cancer, and so could have indicated the presence of a tumour — were from a group of normal blood cells.

Source: www.nature.com