copy number complement

ID: GENO_0000961

A set representing the complement of all copies of a particular biological sequence (typically at the scale of complete genes or larger) present in a particular genome.

The notion of a 'complement' is useful as a special case of a set, where the members necessarily comprise an exhaustive collection of *all* objects that make up some well-defined set. Here, a 'copy number complement' represents 'represents the set of *all* copies of a specified sequence in a particular genome. Note that sequences can be duplicated in a set (i.e. contain more than one member representing the same sequence). In the 'copy number complement' example, each set member is a copy of this same biological sequence.The count of how many of a particular sequences are found in a genome is the sequences 'copy number'. In diploid organisms, the normal copy number for sequences at most locations is 2 (a notable exception being those on the X-chromosome where normal copy number is 1). Variations in copy number occur if this count increases due to a duplication of the gene/region, or decreases due to a deletion of a gene/region. A driving use case for representing copy number is to support associations between variation in copy number of a particular sequence, and phenotypes or diseases that can result. A 'complement' refers to an exhaustive collection of *all* objects that make up some well-defined set. Such a set may contain 0, 1, or more than one members. The notion of a complement is useful for defining many biologically-relevant sets of sequence features, such as 'copy number complements' representing the set of all copies of a particular sequence in a genome. The fact that we are counting how many copies of the same *sequence* exist in a genome here, as opposed to how many of the same *feature*, is what sets sequence-level concepts like 'copy number complement' apart from feature-level concepts like 'single locus complement'. To illustrate the difference, consider a duplication event that creates a new copy of the human APOE gene on a different chromosome. This creates an entirely new sequence feature at a distinct locus from that of the original APOE gene. The 'copy number complement' for sequence defined by the APOE gene locus would have a count of three, as this sequence is present three times in the genome. But the 'single locus complement' at the APOE gene locus would still have a count of two - because the duplicated copy is at a different location in the genome, and therefore does not represent a copy of the APOE locus.