Two terms commonly used in the study of genetics. They were coined by Wilhelm Johannsen in the early part of the twentieth century, but what do they mean, and what is their relationship to each other?
Wilhelm Johannsen (1857-1927) was a Danish botanist, and towering figure in the history of genetics. From his studies with bean plants he coined the terms "phenotype" and "genotype." And he added another word to the dictionary too! Huge De Vries used the term "pangenes" to describe the theory that inheritance was via discrete particulate elements. Johannsen shortened it to "genes." That's got to be worth a couple of points at least in a quiz game.
Definition of Phenotype
A phenotype is defined as all the observable exterior characteristics or traits of an organism. So to take some of our favourite creatures - humans - these would be things like hair colour, facial characteristics, body size and weight, height, and behaviour. A phenotype is typically due to the influence of a variety of interactions between genes and the environment. In some instances such as height, the phenotype - whether you are tall or small - will be influenced greatly by genetics. If you observe tall people, they tend to come from families where there are other tall people, such as parents or grandparents. But the environment (such as a healthy diet) will also play an important role in the expression of this phenotype. And when scientists talk about 'the environment' in relation to genetics, they are not just referring to things that happen in the home or the outside world. They also mean the cellular and sub-cellular environment - timing and interactions between hormones, genes, cells, transcription factors and other biological components.
The influence of genes on the phenotype of behaviour is less well understood, though there is an immense volume of research actively looking at teasing out the genetic influences on such conditions as autism, bipolar disorder, homosexuality, and even political views.
Definition of Genotype
Unlike the phenotype, a genotype cannot be seen. It is your entire genetic makeup, your genome. But it can also refer to a gene or a set of genes. It's the DNA, the raw material that contributes towards the construction of a phenotype. So far example, red hair colour is the phenotype, and the genotype that contributes to it are the versions of the MC1R gene you inherit from each parent. Each gene has two versions, called alleles. You inherit one version from your father and one from your mother. So the red hair genotype is the combination of alleles you inherit from both parents that contribute to red hair colour.