Genotype and Phenotype Difference

Wilhelm Johannsen, a Danish botanist coined the terms 'genotype' and 'phenotype'. In 1911, he published these terms in his paper Om arvelighed i samfund og i rene linier and his book Arvelighedslærens Elementer. Understanding the difference between both these terms is important to gain knowledge about the theory of evolution via natural selection.

Genotype accounts for the genetic constitution of an individual, i.e., it refers to the actual set of genes present in the organism. For sexually reproducing species, the genetic material comprises DNA, which are contributed to it from the egg and sperm of the respective parents.

Precise molecular mechanisms control the transfer of genes from parents to the offspring. Organisms possessing genes that differ in even one locus are known to have different genotypes. In asexually reproducing organisms, the genetic material is an exact copy of the DNA of its parent, because there is no fusion of egg and sperm.

One genotype example would be Tt, which are the alleles for 'tallness' characteristic. Capital T and small t stand for the dominant and recessive genes respectively, which form the genetic makeup.

Phenotype refers to the observed traits or anatomical features of an individual, such as structure, physiology, and behavior. Physical and behavioral characteristics such as size, shape, color, metabolic activities, etc., all come under phenotype of an organism.

These physical attributes and behavioral characteristics determine the organism's ability to survive and reproduce in the environment. The genotype of an organism determines the phenotype of an organism to a large extent.

A phenotype example would be 'Tt', which will appear as a tall person. The dominant 'T' will result in the physical characteristic of tallness in the person, which is visibly seen.

The genotype of an organism determines majority of its phenotype. Thus, the phenotypes depend on the genes that are inherited. However, genes are not the only factor. The phenotype of an organism is determined by three aspects: the genetic make up received from the parents, the environment, and development stages.

Let's take the example of hair. Presence of hair on the head is determined by the genes of an individual. However, the time period for which the hair will remain on the head will depend on environmental factors like chemicals used on the head, excess sunlight, stress, poor diet, etc. This itself shows that the environment influence plays a role in the phenotype.

There are several organisms which have similar genetic makeup, which may differ in their phenotypes. The best example to explain this point is by considering the case of identical twins. They look alike and have the same genetic make up. (Fertilized egg splits into two, to form identical twin zygotes that grow to form two identical babies).

However, they have different phenotypes, as they do have some differences, although they seem identical. Their parents and close ones can always tell one twin from another. Also, their fingerprints differ. Thus, organisms or individuals can have the same genotype, but have different phenotypes.

Phenotype = Genotype + development in the respective environment

The genotypes play a major role, because the kind of genes inherited determine the organism's susceptibility to contracting a particular disease. This susceptibility inherited from the genes will be visible in the individual in the form of symptoms, which is actually the phenotype.