WHAT IS MULTIFACTORIAL INHERITANCE? (WITH EXAMPLES) - BIOLOGY - 2025

The multifactorial inheritance refers to the manifestation of characters genetic basis depend on the action of multiple factors. That is, the character under analysis has a genetic basis.

However, its phenotypic manifestation depends not only on the gene (or genes) that define it, but on other participating elements. Obviously, the most important non-genetic factor is what we collectively call "the environment."

Environmental components

Among the environmental components that most affect the genetic performance of an individual are the availability and quality of nutrients. In animals we call this factor diet.

This factor is so important that for many “we are what we eat”. Indeed, what we eat not only provides us with sources of carbon, energy and biochemical building blocks.

What we eat also provides us with elements for the proper functioning of our enzymes, cells, tissues and organs, and for the expression of many of our genes.

There are other factors that determine the time, mode, place (cell type), magnitude and characteristics of gene expression. Among them we find genes that do not directly code for the character, the paternal or maternal imprint, the levels of hormonal expression and others.

Another biotic determinant of the environment to consider is that of our microbiome, as well as that of the pathogens that make us sick. Finally, epigenetic control mechanisms are other factors that control the manifestation of hereditary characters.

Does everything have a genetic basis in living beings?

We could start by saying that everything that is heritable has a genetic basis. However, not everything that we observe as a manifestation of the existence and history of an organism is hereditary.

In other words, if a particular trait in a living organism can be linked to a mutation, that trait has a genetic basis. In fact, the very foundation of the definition of a gene is mutation.

Therefore, from the point of view of Genetics, only what can mutate and be transmitted from one generation to the other is heritable.

On the other hand, it is also possible that one observes a manifestation of the interaction of the organism with the environment and that this characteristic is not heritable, or that it is so only for a limited number of generations.

The basis of this phenomenon is better explained by epigenetics than by genetics, since it does not necessarily imply mutation.

Finally, we depend on our own definitions to explain the world. For the point in question, we sometimes call character a condition or state that is the product of the participation of many different elements.

That is, the product of a multifactorial inheritance or of the interaction of a particular genotype with a specific environment, or at a given time. To explain and quantify these factors, the geneticist has the tools to study what is known in genetics as heritability.

Examples of multifactorial inheritance

Most of the traits have a multiple genetic basis. Furthermore, the expression of the majority of each of the genes is influenced by many factors.

Among the characters that we know show a multifactorial mode of inheritance are those that define global characteristics of the individual. These include, but are not limited to, metabolism, height, weight, color, and intelligence and coloration patterns.

Some others are manifested as certain behaviors, or certain diseases in humans that include obesity, ischemic heart disease, etc.

We provide in the following paragraphs only two examples of multifactorial inheritance traits in plants and mammals.

The color of the petals in the flowers of some plants

In many plants the generation of pigments is a similar shared pathway. That is, the pigment is produced by a series of biochemical steps that is common to many species.

The manifestation of color, however, can vary by species. This indicates that the genes that determine the appearance of the pigment are not the only ones necessary for the manifestation of color. Otherwise, all the flowers would have the same color in all the plants.

In order for the color to manifest itself in some flowers, the participation of other factors is necessary. Some are genetic and others are not. Among the non-genetic factors is the pH of the environment where the plant grows, as well as the availability of certain mineral elements for its nutrition.

On the other hand, there are other genes that have nothing to do with the generation of the pigment, which can determine the appearance of color. For example, that of the genes that encode or participate in the control of intracellular pH.

In one of them, the pH of the vacuole of the epidermal cells is controlled by a Na ⁺ / H ⁺ exchanger. One of the mutations of the gene for this exchanger determines its absolute absence in the vacuoles of mutant plants.

In the plant known as morning glory, for example, at pH 6.6 (vacuole) the flower is light purple. At pH 7.7, however, the flower is purple.

Milk production in mammals

Milk is a biological fluid produced by female mammals. Breast milk is useful and necessary to support the nutrition of the young.

It also provides their first line of immune defense before developing their own immune system. Of all the biological fluids it is perhaps the most complex of all.

It contains proteins, fats, sugars, antibodies and small interfering RNAs, among other biochemical components. Milk is produced by specialized glands subject to hormonal control.

The multitude of systems and conditions that determine milk production requires that many genes with different functions participate in the process. That is, there is no gene for milk production.

It is possible, however, that a gene with a pleiotropic effect could determine the absolute inability to do so. Under normal conditions, however, milk production is polygenic and multifactorial.

It is controlled by many genes, and is affected by the age, health, and nutrition of the individual. Temperature, the availability of water and minerals intervene in it, and it is controlled by both genetic and epigenetic factors.

Recent analyzes indicate that no less than 83 different biological processes are involved in the production of cow's milk in Holstein cattle.

In them, more than 270 different genes work together to provide a product, from a commercial point of view, suitable for human consumption.

References

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