The Single Nucleotide Polymorphism Database (dbSNP) and the Structural Variation Database (dbVar) are databases of small-scale and large-scale variations, including single nucleotide variants, microsatellites, indels, and CNVs.
The Database of Genomic Variants is a curated catalogue of structural variation in the human genome. As of 2012, the database contains over 400,000 entries, including over 200,000 CNVs, 1000 inversions, and 34,000 indels.
Mutations are sometimes classified by the size of the altered DNA sequence and, at other times, by the functional effect of the mutation on gene expression. Although classification by size is somewhat arbitrary, it can be helpful conceptually to distinguish among mutations at three different levels:
• Mutations that leave chromosomes intact but change the number of chromosomes in a cell (chromosome mutations)
• Mutations that change only a portion of a chromosome and might involve a change in the copy number of a subchromosomal segment or a structural rearrangement involving parts of one or more chromosomes (regional or subchromosomal mutations)
• Alterations of the sequence of DNA, involving the substitution, deletion, or insertion of DNA, ranging from a single nucleotide up to an arbitrarily set limit of approximately 100 kb (gene or DNA mutations)