23 junio, 2024

Phenotypic variations: what they are, types, causes and examples

What are phenotypic variations?

The phenotypic variations are the observable changes in individuals in 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 individuals of a species present, for example, size, shape, color, abilities, etc. There are also some phenotypes that are not easily observable, such as blood types. These 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 and the tallest individual in the world, any height is possible, it is not an attribute that varies in defined segments, for example, every 10 cm.

Continuous traits are observed as a continuously varying gradient and their graphical 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 only exist at discrete intervals. A very illustrative example is the 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 people can’t: nothing in between.

Causes of phenotypic variations

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 may be influenced by genes, but it is also influenced by diet. In this case, diet is 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. The bacteria that survive will have a “resistant” phenotype, which is because they have the genes necessary to eliminate or prevent 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 on their genes to the next generation and favoring the survival of the species. This is the process of evolution.

In short, organisms with phenotypes beneficial for survival are more likely to reproduce and pass on their genetic information.

In this way, higher and higher percentages of the population will have the genes that benefit the species.

Examples of phenotypic variations

The color of the fur of polar bears, which have adapted to the cold. The diversity of shapes, patterns and colors of the shells of mollusks. The color change of the peppered moth: it uses the bark of birch trees for camouflage, but with pollution, the bark of these trees has darkened. The moth too. A family of 4 members where all are overweight (produced by diets and genetic load). The various breeds of dogs, adapting the coat to areas of intense cold or heat.

References

Lewis, R. Human Genetics: Concepts and Applications. McGraw-Hill Education.
Snustad, D. & Simmons, M. Principles of Genetics. John Wiley and Sons.

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