Phenotype (from Greek pheno-, meaning 'showing', and type, meaning 'type') is the term used in genetics for the composite observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological properties, its behavior, and the products of behavior. An organism's phenotype results from two basic factors: the expression of an organism's genetic code, or its genotype, and the influence of environmental factors. Both factors may interact, further affecting phenotype. When two or more clearly different phenotypes exist in the same population of a species, the species is called polymorphic. A well-documented example of polymorphism is Labrador Retriever coloring; while the coat color depends on many genes, it is clearly seen in the environment as yellow, black, and brown. Richard Dawkins in 1978 and then again in his 1982 book The Extended Phenotype suggested that one can regard bird nests and other built structures such as caddis-fly larvae cases and beaver dams as "extended phenotypes".

 

Wilhelm Johannsen proposed the genotype-phenotype distinction in 1911 to make clear the difference between an organism's heredity and what that heredity produces. The distinction resembles that proposed by August Weismann (1834-1914), who distinguished between germ plasm (heredity) and somatic cells (the body).

 

The genotype-phenotype distinction should not be confused with Francis Crick's central dogma of molecular biology, a statement about the directionality of molecular sequential information flowing from DNA to protein, and not the reverse.