Polygenic Inheritance: Definition, Overview, Meaning, Examples, Plants and Humans

What Is Polygenic Inheritance?

The polygenic pattern of inheritance can also be described as a system whereby several genes each with a small impact influence a given characteristic. Polygenic traits are inherited somewhat differently than the simple Mendelian inheritance, it is rather the multiple genes located on different chromosomes that affect the trait. This leads to what is termed a ‘smooth spectrum’ of phenotypes, which makes it difficult to have distinct classes.

For instance, height, skin colour, and even eye colour are controlled by many genes or polygenic. Height is polygenic because genes responsible for height and its determinant factors are several whereas skin and eye colour depend on the effect of several genes that produce a range of colours. Likewise, in plants and animals, any character, from grain shade in wheat to coat shade in dogs also shows polygenic transmission.

Mechanism Of Polygenic Inheritance

Polygenic inheritance is the type of inheritance that occurs by more than one gene but is only responsible for a single characteristic. The optoplasmic gene has multiple alleles that jointly affect the result in the phenotype of an individual. Most usually, these genes are on separate chromosomes and participate in the development of the trait.

How Multiple Genes Contribute To A Single Trait?

The effects of genes in polygenic models are small and cumulative; that is, the effects of genes on the phenotype are small and they increase in the whole. For example, the height of people is determined by many genes whereas none of the genes is completely responsible for height. The overall expression of all these genes adds up to produce the final phenotype; the phenotype.

Interaction Of Alleles From Different Genes

As such alleles, of different genes combine to form several phenotypes. A gene can exist in more than one form and the different forms when interacting with each other may produce variation in the trait. For instance, variations within the genes controlling skin colour result in variations in skin shade, colour or tone.

Additive Effects Of Alleles

Additivity implies that the relative impact of the individual alleles is summative to produce the phenotype of an organism. Therefore, while dominant alleles could contribute a quantity to the trait, recessive alleles contributed lesser quantities. When the dominant alleles are invigorated, then the organism is characterized by a more intensified feature. For example, in human height, the dominant alleles contained in a person means that they are most likely to be taller, the more alleles that point towards a certain height an individual has, the taller he or she is likely to be.

Examples Of Polygenic Inheritance

The examples are-

Human Height

The human height good example of an inherited trait that is polygenic. This is because it depends on the summed-up impact of several genes, all of which make relatively small contributions towards height. Some of the key genes that are affected are the ones that are related to growth hormones, and bone formation. These genes can also be variable and do not directly cause one to fit into either tall or short but are rather on a continuum.

Skin Colour

The shade of your skin is defined by the activity of several genes that regulate the production of melanin. The colour of skin depends on the pigment called melanin whose synthesis is controlled by the genes such as MC1R, SLC24A5, and SLC45A2. The phenotypes of the skin colour arise from the delayed intermingling of the alleles of this gene.

Eye Colour

Most people believe that eye colour is determined by a single gene, but there is more than one gene associated with eye colour, the prime genes are OCA2 and HERC2, the genes control the amount and sort of pigments present in the iris of the eye. This interaction between these genes defines the end look of one’s eye colour which can be brown, blue, green, hazel or any other colour with different shades and different intensities.

Weight And Body Shape

Fatness and body mass are determined by the various genes that affect metabolism rate, body fat pattern and hunger. Specific genes including FTO, and MC4R are associated with obesity and the distribution of body fat. Thus, the genetic influences are further mitigated by other factors such as diet and exercise in determining a person’s weight and physique.

Polygenic Inheritance And Evolution

The Impact of polygenic Inheritance on evolution is described below-

Contribution To Evolutionary Processes

When it concerns the evolution of populations, polygenic inheritance plays an important role as it leads to variabilities within the population. There is a continuous modification of traits resulting from multiple gene combinations which consequently offer an array of phenotypes. Such diversity is beneficial for the populations to be able to cope with the new conditions and selective pressures as they change in future.

Natural Selection And Polygenic Traits

Natural selection’s impact on a population pertains to polygenic traits where certain individuals inherit good alleles for those particular traits. Polygenic traits are linked with many genes hence the selection pressure causes variations in the combination of alleles within a population. For instance, if a given height or skin colour relieves a person from high risks of being attacked by predators or getting sunburnt among others, this characteristic is passed on to the next generations.

Adaptive Significance Of Polygenic Traits

Polygenic characters usually have adaptative value because characters that are developed in response to variation can be changed gradually in small steps which are most appropriate to finely tune the response to the environment. For instance, skin colouration enables people to cope with UV radiation at different levels in different geographical locations, and body sizes and shapes also contribute to our survival in various climatic conditions. Such changes are beneficial in increasing the advantage of an organism’s fitness in certain habitats and the overall genetic stock of the population.

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