All are types of genetic polymorphism, except

Genetic polymorphisms (variations) result when copies of a specific gene present within a population do not have identical nucleotide sequences.The term allele refers to one of a series of alternative DNA sequences for a paicular gene. In humans, there are 2 copies of every gene. An individual's genotype for a given gene is determined by the set of alleles that the individual possesses. The most common form of genetic variation involves a single base change at a given location, referred to as a single-nucleotide polymorphism (SNP). At the other end of the spectrum are copy number variations, which refer to the deletion or duplication of identical or near identical DNA sequences that may be thousands to millions of bases in size.Reference: Nelson Textbook of Paediatrics; 20th edition; Chapter 59; Pediatric Pharmacogenetics, Pharmacogenomics, and Pharmacoproteomics