Where sections of the genome have been duplicated. This can be short sections only a few bases long, or large tracts several kilobases long.
Use in clinical context
Duplications in the genome can vary in size and have a range of effects. The size of duplication, however, does not necessarily correspond to the size of the effect.
Duplications within genes can be small, but even small changes can alter the amino acid sequence of the resulting protein, changing its function. Other duplications, however, may have little apparent impact on phenotype.
Some duplications may copy whole genes or chromosomes, resulting in extra protein being produced which can have dramatic phenotypic consequences.