Phenotype

A phenotype is any observed quality of an organism, such as its morphology, development, or behavior, as opposed to its genotype - the inherited instructions it carries, which may or may not be expressed. 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.
Despite its seemingly straightforward definition, the concept of the phenotype has some hidden subtleties. First, most of the molecules and structures coded by the genetic material are not visible in the appearance of an organism, yet are part of the phenotype. Human blood groups are an example. So, by extension, the term phenotype must include characteristics that can be made visible by some technical procedure. A further, and more radical, extension would add inherited behaviour to the phenotype.

Biston betularia morpha typica, the standard light-coloured Peppered Moth.

Biston betularia morpha carbonaria, the melanic Peppered Moth, illustrating discontinuous variation.
Second, the phenotype is not simply a product of the genotype, but is influenced by the environment to a greater or lesser extent (see also phenotypic plasticity). And, further, if the genotype is defined narrowly, then it must be remembered that not all heredity is carried by the nucleus. For example, mitochondria transmit their own DNA directly, not via the nucleus, though they divide in unison with the nucleus.
The phenotype is composed of traits or characteristics Some phenotypes are controlled entirely by the individual's genes. Others are controlled by genes but are significantly affected by extragenetic or environmental factors. Almost all humans inherit the capacity to speak and understand language, but which language they learn is entirely an environmental matter.