Phenotypic variation describes different trait expressions of individuals with the same genotype. The principle was popularized 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 phenotypic variation?
By phenotypic variation, biology refers to the different trait expressions between individuals of the same species. Phenotype refers to the actual appearance of an organism, including all the individual characteristics of an individual. Instead of morphological traits, the term refers to physiological and behavioral traits. The phenotype does not depend exclusively on genetic characteristics of an organism, but is mainly determined by environmental influences. By phenotypic variation, biology refers to the different trait expressions between individuals of the same species. Despite sharing a common genotype, individuals take on different phenotypes due to environmental influences. The principle of phenotypic variation dates back to the observations of Frenchmen Georges Cuvier and Étienne Geoffroy Saint-Hilaire. In Great Britain, it was first described by Erasmus Darwin and Robert Chambers. Charles Darwin eventually made phenotypic variation more widely known, but is not considered the first describer of the phenomenon according to current knowledge. He used the term divergence in connection with phenotypic variation, describing the fact that phenotypic individual characteristics increase steadily with generations and that individual representatives of a race move further and further away from the racial characteristics.
Function and task
Mendel’s rules explain phenotypic variation in simple terms. Mendel studied the inheritance of individual traits in plants. For example, he observed the color of flowers and crossed plants with red and white hues with each other. The phenotypes of the individuals thus bred were either red or white. The genotype of the plants contained the information for red as well as white flowers for all offspring. Thus, the enforcement of a hue could not be foreseen from the genotype alone. Phenotypic variation is not determined by genetic mutation, but can result in mutation over the generations. From a genome the later phenotype cannot be read off unambiguously. Nor can a specific genotype be inferred unambiguously from the phenotype. The genotype-phenotype relationship thus remains relatively unclear. According to Darwin’s synthetic theory of evolution, minute changes in phenotype become manifest trait changes in the course of evolution, which can progress to species change. Mutation-induced changes in a phenotype can be accompanied by a geographic selection advantage, resulting in two geographically restricted subvariants of the same species that persist side by side. An example of this is lactose persistence, which allowed northern Europeans to metabolize animal milk thousands of years ago. Evolutionary developmental biology lists complex discontinuous spontaneous variation in the same generation alongside continuous variation in phenotype. All species exhibit phenotypic variation. Variations are not an exception, but correspond to the rule. Variation in particular traits within the same species is not spatially uniformly distributed. Different populations often exhibit variability, for example, individuals with different body sizes. All phenotypic variation among populations of a species provides evidence of evolutionary processes. Phenotypic variation is a cornerstone of natural selection and thus provides survival advantages to individuals in different environments. The differences between human eye and hair colors are among the best known examples of variation within the human species. Meanwhile, in species such as the zebra, the principle of phenotypic variation appears, for example, in the stripe differences among zebra species. Burchell’s zebras have about 25 stripes, mountain zebras have about 4o, and Grevy’s zebras even have around 80.
Diseases and ailments
Within the human species, countless examples of phenotypic variation exist. Some of these are associated with disease. Sickle cell anemia, for example, is the result of phenotypic variation.This disease brings about a sickle-shaped deformation of red blood cells, which is accompanied by circulatory disorders. Sickle cell anemia is not only a disease, but at the same time a curative variation. The deformation of red blood cells is accompanied by resistance to malaria. This malaria resistance meant evolutionary biological advantages and withstood natural selection in this way. Phenotypic variation evolved into a mutation that is still prevalent in the human species today. Among the best-known examples of the advantages of phenotypic variation is human lactose tolerance. Originally, the human species was unable to metabolize milk and dairy products outside of infancy. This lactose intolerance disappeared over time through phenotypic variation for almost all individuals in northern Europe. Since the ability to metabolize milk and dairy products was associated with significant evolutionary advantages for humans, the phenotype took retroactive effect on the genotype through a genetic mutation. Since then, lactose tolerance has been considered the norm for northern European humans. Nevertheless, at the same time phenotypes with the original lactose intolerance persist within the human species. Beyond these correlations, phenotypic variation also plays a role in diseases, especially in hereditary disease patterns. The longer a particular disease has been prevalent in a species, the more likely phenotypic variation of the same disease will occur. In this way, the same disease pattern can produce a wide variety of symptoms after several generations. The subtypes of a disease can thus be used to approximate how long the disease has been prevalent in a species. Phenotypic variation also occurs in hereditary diseases, which only develop as a result of certain exogenous factors. Cancer, for example, may be inherent in the genotype but still does not reach outbreak in every phenotype.
