The phenotypic variation describes different characteristics of individuals with the same genotype. The principle was made known by the evolutionary biologist Darwin. Diseases such as sickle cell anemia are based on phenotypic variation and were originally associated with an evolutionary advantage.
What is the phenotypic variation?
The phenotype describes the actual appearance of an organism including all individual characteristics of an individual. Instead of referring to morphological characteristics, the term refers to physiological characteristics and behavioral characteristics. The phenotype does not only depend on the genetic properties of an organism, but is primarily determined by environmental influences.
With the phenotypic variation, biology refers to the different characteristics between individuals of the same species. Despite the common genotype, the individuals adopt different phenotypes due to environmental influences.
The principle of phenotypic variation goes back to the observations of the French Georges Cuvier and Étienne Geoffroy Saint-Hilaire. It was first described in Great Britain by Erasmus Darwin and Robert Chambers. Charles Darwin finally made the phenotypic variation better known, but according to current knowledge is not considered to be the first to describe the phenomenon. In connection with the phenotypic variation, he used the expression of divergence and thus described that phenotypic individual traits steadily increase with the generations and that individual representatives of a race move further and further away from the racial traits.
Function & task
Mendel's rules explain the phenotypic variation in simple terms. Mendel examined the inheritance of individual characteristics in plants. For example, he observed the color of the flowers and crossed plants of red and white tones with each other. The phenotypes of the individuals so bred were either red or white. The genotype of the plants contained the information for red and white flowers for all offspring. The enforcement of a color was therefore not foreseeable from the genotype alone.
Phenotypic variation is not determined by genetic mutation, but can lead to mutation over the generations. The later phenotype cannot be clearly read from a genome. Nor can a specific genotype be clearly deduced from the phenotype. The relationship between genotype and phenotype remains relatively unclear.
According to Darwin's synthetic theory of evolution, the smallest changes in the phenotype become manifest changes in characteristics in the course of evolution, which can range up to species change. Mutation-related changes in a phenotype can be associated with a geographic selection advantage and result in two geographically limited sub-variants of the same species that remain side by side. One example of this is lactose persistence, which thousands of years ago allowed northern Europeans to metabolize animal milk.
In addition to the continuous variation of the phenotype, evolutionary developmental biology lists complex, discontinuous spontaneous variations in the same generation. All species have phenotypic variations. Variations are no exception, they are the norm. The variation of certain characteristics within the same species is not evenly distributed spatially. For example, different populations often exhibit variability, such as individuals with different body sizes. All phenotypic variations of the populations of a species prove the evolutionary processes.
The phenotypic variation is a cornerstone of natural selection and thus gives individuals in different milieus advantages for survival. The differences between human eye and hair colors are the most well-known example of variation within the human species. In species such as the zebra, the principle of phenotypic variation appears, for example, in the stripe differences of the zebra species. Burchell's zebras have around 25 stripes, mountain zebras around 40 and Grevy's zebras even around 80.
Illnesses & ailments
There are innumerable examples of phenotypic variation within the human species. Some of them are associated with diseases. Sickle cell anemia, for example, is the result of phenotypic variation. This disease produces a sickle-shaped deformation of the red blood cells, which is associated with circulatory disorders. Sickle cell anemia is not only a disease, but also a curative variation. Resistance to malaria goes hand in hand with the deformation of red blood cells. This malaria resistance meant evolutionary advantages and thus withstood natural selection. A mutation developed from the phenotypic variation that is still common in the human species to this day.
The best known example of the benefits of phenotypic variations is lactose tolerance in humans. Originally, outside of infancy, the human species was unable to metabolize milk and dairy products. This lactose intolerance disappeared over time due to phenotypic variation for almost all individuals in Northern Europe. Since the ability to metabolize milk and milk products was associated with significant evolutionary advantages for humans, the phenotype had a retroactive effect on the genotype through a genetic mutation. Since then, lactose tolerance has been considered the norm for northern European people. Nonetheless, at the same time, phenotypes with the original lactose intolerance persist within the human species.
In addition to these relationships, phenotypic variation also plays a role for diseases, especially for hereditary clinical pictures. The longer a particular disease has been spread in a species, the more likely it is to have phenotypic variations of the same disease. In this way, the same clinical picture can cause a wide variety of symptoms after several generations. Using the subtypes of a disease, it is possible to roughly understand how long the disease has been spreading in one type.
Phenotypic variation also occurs in hereditary diseases that can only be triggered by certain exogenous factors. Cancer, for example, can be inherent in the genotype, but still does not break out in every phenotype.
