Polygenic inheritance is the expression of a quantitative trait in which multiple non-allelic genes from different loci of different chromosomes mutually effect. Here we are going to discuss polygenic inheritance examples in brief.
Polygenic inheritance example in plants-
Polygenic inheritance example in humans-
Let’s have a closer look at polygenic inheritance example in plants.
Colour and shape of corolla
The colour and shape of corolla is very common polygenic inheritance example. Multiple genes from different chromosomes are involved in expression of that particular trait additively. From examples in the case of Nicotiana longiflora, or common name tobacco, the length of its corolla shows polygenic inheritance. About 5 different non-allelic genes are additively expressed and affect the phenotype.
Polygenic inheritance is very common in the case of flowers. From the number of bract to size of ray, colour of petals all commonly shows polygenic inheritance. In case of sunflower or Helianthus sp. Size of the bract shows polygenic inheritance extremely. In the case of Bidens pilosa the head of compositae is another example of polygenic inheritance.
Fruit size and colour
Another polygenic inheritance example is fruit size and colour. Several non-allelic genes from different loci of chromosomes are involved in expression of a single trait. In the case of red chilli pepper or Capsicum species the colour and size of fruit shows polygenic inheritance. Another common example is the kernel colour of wheat. Three differently assorted allele pairs are involved together to express the trait. If only the dominant trait expressed the wheat gets its red colour and if the recessive traits are expressed then it gets the white colour. Apart from this several intermediate variations are found due to the effect of different polygenes.
Size of seed
The size and colour of seed is also an example of polygenic inheritance. The ear size of grain is another example of quantitative polygenic inheritance, in which multiple non-allelic genes are involved.
Seed oil content
Polygenic inheritance is also shown in case of seed oil content of some plants. Several genes additively affect the phenotypic trait. The seed oil content of Brassica napus L. Is influenced by several different genes, hence shows polygenic inheritance.
The size, colour of pollen in many plants shows polygenic inheritance. More than one gene additively affects one particular trait. Hence a wide range of variations in pollen size and colour is shown.
Time of maturation
The time of maturation of fruit, seeds are examples of polygenic inheritance. Several non-allelic genes additively affect the phenotypic trait.
Let’s have a closer look at polygenic inheritance examples in humans.
Skin colour of human
The skin colour in humans is a very common example of polygenic inheritance. The most important factor which controls the skin complexion in humans is the synthesis of skin pigment melanin. The amount of melanin makes the skin darker. Several non-allelic genes are involved together to express the trait. Along with the melanin deposition environmental factors also influence skin colour.
Human Eye colour
As like the skin colour melanin composition also influences eye colour in humans. The amount of melanin in the front of the iris determines the eye colour. 16 different genes are involved in expression of the trait, two of which are located at the chromosome 15 (OCA2 and HERC2). More melanin makes the eye colour darker. People with more melanin composition in iris have darker brown or black coloured eyes.
Human Hair colour
Human hair colour is also inherited Polygenic Traits, meaning multiple non-allelic gene expressions are associated with the trait. Melanin pigment plays a crucial role in it. There are three different melanin present in the human body such as Eumelanin, Pheomelanin and Neuromelanin. If Eumelanin deposited through the activation
of Melanocortin 1 Receptor (MC1R), it causes darker hair colours. When Melanocortin 1 Receptor (MC1R) is inactivated then Pheomelanin deposited causes lighter hair colour. As the melanin composition acts as a protector from UV sun rays, people with darker hair color gets more protection than the lighter hair colour.
Human height is also explained as a polygenic inheritance example, because it is also controlled by multiple numbers of different genes. In a recent study it is found that about 697 genetic variants in 423 genetic loci are involved together to express the phenotypic trait of human height. That’s why a wide range of variation is noted in the population.
Another very common polygenic inheritance example is weight of a human. Whenever discussing the human weight topic, we focus a lot on the environmental factors like malnutrition, presence of diseases, amount of food intake, BMR, etc but polygenes play a major role in it also. In some people it is noted that the kind of obesity they have are actually caused by the additive effect of multiple non-allelic genes. But this kind of obesity is rare in population.
Polygenic inheritance is also shows in the intelligence or IQ of a person. According to a recent study it is found that more than 500 non-allelic genes are additively effective to express the trait. Hence a wide range of spectrum is created among all. Though the IQ or intelligence of a person is also influenced by several environmental factors also.
Just like the body weight the body shape of a person is also a result of polygenic inheritance. Different genes from different loci of chromosomes are involved and influence the trait to express. Apart from polygenes environmental factors also play a major role in determining the body shape of a person.
So here are some very common polygenic inheritance examples in which multiple non-allelic genes additively influence to express the trait.
Polygenic inheritance example from publicdomainpictures.net
What is polygenic inheritance?
In simple words Inheritance which is caused by the cumulative expression of polygenes, is called polygenic inheritance.
Polygenic inheritance is a quantitative inheritance caused by more than one non-allelic gene expression. For example , human height, human body shape, skin colour, etc are the polygenic inheritance examples.
Polygenic inheritance shows a wide range of intermediate variations, more than dominant or recessive trait expressions among the population. In polygenic inheritance every involved gene is expressed equally and the mixture or additive effect is expressed through the phenotype. It doesn’t follow the Mendelian inheritance law. The Mendelian law is all about the monogenic inheritance which focuses one the expression of dominant and recessive traits.
Characteristics of polygenic inheritance
As polygenic inheritance is one of the most common inheritance found in most of the organisms from plants to humans, here we are going to discuss about the characteristics of it.
- More than one gene or we can say multiple non-allelic genes are involved to express one phenotypic trait.
- Every single gene influences the trait cumulatively means the concept of dominance is not acceptable here.
- As several genes additively influence the trait each of them employs minor effects. The detection of those minor effects separately is often difficult.
- Epistasis is not found means, one gene expression cannot be masked by another gene expression.
- A wide range of intermediate variations are possible in polygenic inheritance. It shows a wide spectrum where most of the population consists of the intermediate trait or middle range of the curve.
- The statistical analysis of polygenic inheritance is not as simple as Mendelian inheritance law. The pattern is very complex, and can not be predefined.
- Polygenic inheritance is different from codominance where multiple alleles on the same locus are expressed additively. Just like the human blood group system.
Polygenic inheritance gene types
In polygenic inheritance we can see that multiple non-allelic genes from different loci of chromosomes are involved together or expressed together. According to the nature of expression genes participating in polygenic inheritance are two types, the first one is contributing genes and another is non-contributing genes.
- Contributing genes or alleles: These genes or alleles are polygenes which express and contribute to the continuous variation of polygenic inheritance. It is also known as the effective gene or effective alles.
- Non-contributing genes or alleles: These are genes or alleles which do not contribute to continuous variation of polygenic inheritance. These genes or alleles are also known as non-effective genes or alleles.
To know more about genes read our article on DNA Structure | A detailed insight with all crucial aspects
Polygenic inheritance in plants
Polygenic inheritance is very common in case of plants. Several non-allelic genes are involved together to express a single phenotype. Colour and shape of corolla, colour and shape of fruits, seeds, oil content of seeds, time of maturation, etc all are examples of polygenic inheritance in plants. All in this case more than one non-allelic gene is involved and influences the trait.
Polygenic inheritance skin colour
The skin colour in humans is a very common example of polygenic inheritance.
The most important factor which controls the skin complexion in humans is the synthesis of skin pigment melanin. The amount of melanin makes the skin darker. Just like Albino people do not contain melanin in their skin at all. The melanin apart from darkening the complexion gives protection to the skin from the harmful UV-rays of sunlight.
Along with the melanin deposition environmental factors also influence melanin synthesis as well as the skin colour. That’s why mostly fair people go for the sunbath and so that the melanin synthesis increases in their skin.
Polygenic inheritance example from Wikimedia Commons
Is blood type polygenic inheritance?
In the human blood system more than one allele is expressed.
The blood type is not polygenic inheritance. In the blood group three different alleles from the same loci are expressed which are IA, IB and IO which is an example of codominance. But in polygenic inheritance multiple non-allelic genes from different loci of chromosomes are involved to express a trait.
To know more read our article on Chromosome Structure: Detailed Explanations
As a whole we can say that polygenic inheritance plays a crucial role in the evolution of organisms. It helps to increase variations among species. Here we discuss polygenic inheritance example in brief. We also give some ideas about the characteristics and types of polygenic inheritance. Hope the article will be helpful to you.