The phenotypic variations are observable changes in individuals of a population caused by genes, environmental factors or a combination of both. Phenotypic variations in a population can contribute to natural selection and evolution.
Phenotypes are the traits or characteristics that organisms possess, for example: size, shape, color, capabilities, etc. There are also some phenotypes that are not easily observable, for example: blood types are phenotypes that can only be determined using laboratory techniques.
Types of phenotypic variations
Basically, there are two types of phenotypic variations: those that are continuous and those that are not, the latter are also called "discrete" because they vary at discontinuous intervals.
Height and color are two examples of continuous phenotypic variations, that is, between the smallest individual and the tallest in the world, any height is possible, it is not an attribute that varies in defined segments, for example: every 10 cm.
Continuous features are seen as a continuously varying gradient and their graphic representation is bell-shaped, with intermediate phenotypes being the most common. This is a good way to recognize continuous variation.
In contrast, some phenotypes vary discontinuously and exist only at discrete intervals. A very illustrative example is blood type, which can be A, B, AB, or O, but there is no intermediate phenotype for blood. Another example is the ability to curl the tongue, some people can and some cannot, nothing in between.
Causes
As mentioned above, phenotypes can be caused by genes, environmental factors, or an interaction between the two. Environmental factors are all those elements of the environment that can influence organisms in various ways.
For example, body weight in humans can be influenced by genes, but it is also influenced by diet. In this case, diet is an example of an environmental factor. The effects that environmental factors have on phenotypes are difficult to pin down, as there are many possible factors that must be considered.
Another very important example, if you treat a group of bacteria with an antibiotic, some will survive and some will not. Bacteria that survive will have a "resistant" phenotype, which is because they have the genes necessary to eliminate or avoid the effects of the antibiotic.
Bacteria without that particular gene will be susceptible to the antibiotic and will not survive, this phenotype is called "sensitive."
Thus, only resistant bacteria will be able to survive and reproduce, passing their genes to the next generation and favoring the survival of the species, this is the process of evolution.
In summary, organisms with phenotypes that are beneficial for survival are more likely to reproduce and pass on their genetic information.
In this way, increasingly higher percentages of the population will have the genes that benefit the species.
References
- Forsman, A. (2014). Effects of genotypic and phenotypic variation on establishment are important for conservation, invasion, and infection biology. Proceedings of the National Academy of Sciences, 111 (1), 302–307.
- Fox, C., Roff, D. & Fairbairn (2001). Evolutionary Ecology: Concepts and Case Studies. Oxford University Press.
- Griffiths, A., Wessler, S., Carroll, S. & Doebley, J. (2015). Introduction to Genetic Analysis (11th ed.). WH Freeman.
- Hallgrímsson, B. & Hall, B. (2005). Variation: A Central Concept in Biology. Elsevier Academic Press.
- Lewis, R. (2015). Human Genetics: Concepts and Applications (11th ed.). McGraw-Hill Education.
- Moussean, T., Sinervo, B. & Endler, J. (2000). Adaptative Genetic Variation in the Wild. Oxford University Press, Inc.
- Snustad, D. & Simmons, M. (2011). Principles of Genetics (6th ed.). John Wiley and Sons.