 To make sense of the original meanings of the terms and the distinction between them as well as the coexistence of different kinds of meanings since then, a specific kind of abstraction (see entry on  abstract objects)  is pertinent, namely, the material practices of control over biological materials and conditions advanced in modern experimental biology and agricultural breeding or entailed in the allied use of models in analysis of data. Reliable methods more than endorsable theories are the touchstone of this kind of abstraction. It is within a framing of control—and the consequent challenge of reintegration—that this entry discusses the other senses already mentioned of the terms genotype and phenotype: in the context of the relationship between an individual’s DNA and traits; what the use of the terms signifies; and grouping into classes. (Given the continuing coexistence of the different kinds of meaning of the terms, qualifiers are used when there might be ambiguity.)