genomic sequence set functional copy complement A set representing the complement of all functional versions of a specified sequence (typically that of a gene) in a particular genome. 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 the set of all functional copies of a particular sequence in a genome. This is known as the 'functional copy number' or 'genetic dosage' of the sequence. 'Functional copies' of a sequence are those that exhibit normal activity and/or produce gene products that exhibit normal activity associated with the sequence. The count of functional copies of a gene is often referred to as its 'dosage'. In diploid organisms, the normal 'dosage' is 2 for autosomal genes/regions. Dosage increases if there is a duplication of a functional gene/region. Dosage decreases if there is either a deletion of a gene/region, or an inactivating mutation that eliminates gene function. This sets it apart from the notion of a 'copy number complement', which reflects how many copies of a sequence exist in a genome, regardless of their functionality. Addition of a non-functional allele of a gene will increase its copy number, but not increase its dosage. As we saw for 'copy number complement', the defining sequence here is specified in terms of a location on a reference sequence - typically the location where a gene or set of genes resides. But the criteria for membership in a 'functional' copy number complement require only that the feature can perform the functions associated with the gene or genes at the defining location. A gene allele that varies by only one nucleotide from the wild-type gene may not qualify as functional if that alteration eliminates the activity of the allele. functional genetic dosage