1) Class within a class 2) Group within a group 1) Subtyping 
A type S is a subtype of type T if every valid operation on an object of type T is also a a valid operation of type S.
a genetic variation of an organism. Subtypes are a more narrow classification than genotypes, but broader than quasispecies. Genotype 1 HCV is divided into subtypes 1a and 1b.
A genetic variant.
also called a clade. With respect to HIV isolates, a classification scheme based on genetic differences.
a subordinate type. · a special type included within a more general type.