Mutations are changes in genetic information and can be the cause of numerous diseases. They can occur at the level of the genome, the chromosomes or the gene. In the case of genome mutations, entire chromosomes are either duplicated or lost. An example of a widespread genome mutation is the triple occurrence of chromosome 21, leading to Down syndrome (trisomy 21). Chromosome mutations affect larger segments of a chromosome, for example if the sequence of individual genes on a chromosome is altered (rearrangement), segments are lost (deletion) or doubled (duplication).
If a change in a gene is present, this is referred to as genetic mutation. Genetic mutation is an inheritable change in the DNA sequence which comes about as a result of the substitution of one base pair for another (point mutation), the loss of base pairs (deletion) or the addition of base pairs (insertion).
Point mutations, also known as single nucleotide polymorphisms or SNPs (pronounced "snips"), are the most significant. Such variants of specific bases are crucial in determining the genetic difference between individuals. In some cases they can remain unnoticed, but sometimes they can also affect the carrier's state of health.
Mutations that occur spontaneously in nature should be distinguished from targeted changes made to DNA using bioengineering techniques.

Furthermore, a distinction should be made between mutations in the germ track and so-called somatic mutations. The former involve germline cells, i.e. oocytes and spermatozoons, and are inherited by all possible descendants. Somatic mutations, on the other hand, only affect the DNA of somatic cells; while they can have sometimes significant implications for the affected subject, they are not passed on to descendants.