A phenotype is any observable characteristic of an organism, such as its morphology, evelopment, biochemical or physiological properties, or behavior. Phenotypes are influenced by a combination of genetic and environmental factors. This contrasts with the genotype of an organism - the inherited instructions it carries - which may or may not cause an observable effect on the organism. This genotype-phenotype distinction was proposed by Wilhelm Johannsen in 1911 to make clear the difference between an organism's heredity and what that heredity produces. The distinction is similar to that proposed by August Weismann, who distinguished between germ plasm (heredity) and somatic cells (the body). A more modern version is Francis Crick's Central dogma of molecular biology.