classification system categorizing organisms by genetic traits; including full hereditary info or part of genomic sequences, they are one of the three factors that determine phenotype. Organisms of the same genotype cluster in phylogenetic trees

The genotype is the genetic constitution of an organism, mainly its genome.[1] The term is contrasted with the term phenotype, as follows:

genotype + environment → phenotype

The terms were invented by Wilhelm Johanssen to distinguish between inherited and environmentally produced variation.[2] "The distinction was not new. It had, for instance, been discussed by Francis Galton as nature vs. nurture.[3]

The extent to which the genotype influences the phenotype varies hugely. Some aspects of the phenotype are almost entirely determined by heredity, such as eye colour and blood types. Human language is an interesting case. The capacity to learn and speak a language is entirely inherited, but which language is spoken is entirely learnt, and hence is environmental.


  1. King R.C. Stansfield W.D. & Mulligan P.K. 2006. A dictionary of genetics, 7th ed. Oxford. p179
  2. Johannsen W. 1911. The genotype conception of heredity. American Naturalist 45, 129-159
  3. Sturtevant A.H. 1965. History of genetics. Harper & Row, N.Y. p59