Phenotype

The term phenotype was coined by the Danish botanist and geneticist Wilhelm Ludvig Johannsen and is used to describe an individual organism either through its total physical appearance and/or constitution, or a specific manifestation of a particular trait such as the size, eye color, or variations in behavior.

The concept developed by Johannsen, now accepted by medical researchers around the world, was that individual organisms had a “genotype” made up from their DNA which is inherited from their parents. Although Johannsen worked initially on plants, much research has been conducted on animals, and most of the work has been on human beings. Obviously, phenotypes are determined, to a large extent, by the genotype of the person, but environmental and behavioral factors can also be important and these can result in phenotypes whereby people look, act, or feel different to their parents. There may also be random variations, and this has meant that the relationship can essentially be summarized as a person's phenotype is made up from his or her genotype (inherited characteristics), his or her environment and behavior, and some element of random variations. As a result, people who suffer from cancer may do so as a result of a genetic predisposition, from their environment (such as exposure to radiation), their behavior (such as smoking), and also random factors.