sequence role reference sequence A reference sequence is one that serves as a standard against which 'variant' versions of the feature are compared, or against which located sequence features within the reference region are aligned in order to assign position information. Being 'reference' does not imply anything about the frequency or function of features bearing the sequence. Only that some agent has used it to serve a reference role in defining a variant or locating a sequence. A sequence that serves as a standard against which other sequences at the same location are compared. The notion of a 'reference' in GENO is implemented at the level of 'biological sequence' rather than at the level of a sequence feature - i.e. we define a class for 'reference sequence' rather than reference sequence feature'. This is because it is at the *sequence* level that features of interest are determined to be variant or not. It is taken for granted that the *location* of the feature of interest is the same as that of the reference sequence to which it is compared, becasue an alignment process establishing common location always precedes the sequence comparison that determines if the feature is variant. reference sequence reference biological sequence