The occurrence post-fertilisation of two or more cell lines with different genetic or chromosomal constitutions within a single individual or tissue, occurring as the result of an error in cell division or a new mutation.
A helpful clinical clue is that people with a genetic condition due to mosaicism may have disturbances of skin pigmentation - whorls, swirls or lines, particularly along the lines of Blashko but these may be very faint. Sometimes it may be possible to detect two populations of cells with different chromosome constitutions 9where this is the cause) by performing a skin biopsy.
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