An individual polygenic is one of a group of non-epistatic genes that interact additively to influence a particular trait, thereby contributing to multiple-gene inheritance (also known as polygenic inheritance, multigenic inheritance, or quantitative inheritance), a type of non-Mendelian inheritance that differs from the single-gene inheritance, which is the fundamental concept of Mendelian inheritance. Because it is often difficult to distinguish the effect of a single gene from the effects of other genes and the environment on a particular phenotype, the term “monozygous” is commonly used to refer to a hypothetical gene.
Polygene
Statistical methodology and high-throughput sequencing, on the other hand, have advanced to the point where researchers are able to identify candidate genes for the trait. When a gene for a quantitative trait is discovered, it is referred to as a quantitative trait locus (QTL). These genes are also generally pleiotropic in their effects.
Polygenes are thought to be the majority of the genes that contribute to type 2 diabetes development. In July 2016, scientists announced that they had discovered a set of 355 genes that belonged to the last universal common ancestor (LUCA) of all organisms that have ever lived on Earth.
Traits with polygenic determinism correspond to the classical quantitative characters, whereas qualitative characters with monogenic or polygenic determinism correspond to the classical quantitative characters. In essence, rather than having only two options, such as freckles or no freckles, there are many variations, such as the colour of skin, hair, or even the colour of eyes, to choose from.
Polygenic Inheritance characteristics
- A polygenic is a gene that, when combined with other genes, has a small effect on a phenotype’s expression.
- Because the effect of a single gene is so small, it is difficult to detect its presence.
- A number of genes have the same effect on the body.
- Each allele has a cumulative or additive effect on the other alleles.
- Polygenic inheritance differs from multiple allele inheritance in that, in multiple allele inheritance, three or more alleles are present in the same locus of which any two alleles are present in an organism, such as the ABO blood group system, which is controlled by three alleles. Polygenic inheritance, on the other hand, is not controlled by three alleles.
- Neither epistasis nor the masking of the expression of an allele from a different locus is involved in this process.
- There is no evidence of linkage or dominance; rather, there are alleles that contribute and alleles that do not contribute, which are referred to as active and null alleles, respectively.
- It is characterised by the continuous variation of a trait’s phenotype, which is known as polygenic inheritance.
- The pattern of polygenic inheritance is complicated. It is difficult to predict the phenotype of an organism.
- The statistical analysis can provide an estimate of the parameters of a population.
Polygenic Inheritance in Humans
Polygenic inheritance can be observed in many human characteristics, including skin and hair colour; height; eye colour; the likelihood of developing diseases and developing resistance; intelligence; blood pressure; bipolar disorder; autism; longevity; and many more.
A brief description of some of the characteristics is as follows:
Height:
There are approximately 400 genes that are responsible for the phenotype, and the environment has a significant impact on the expression of these genes.
Eye colour:
Polygenes play a role in determining the colour of the eyes. Humans are capable of distinguishing between at least nine different eye colours. There are two major genes that influence eye colour, as well as 14 additional genes that influence the expression of the phenotype. In order to achieve each colour, a different number of alleles must be present. These have been discovered to be X-linked.
Polygenic Inheritance in Plants
Polygenic inheritance in plants includes traits such as the colour and shape of the stem, pollen, flower, yield, oil content, seed size, and the amount of time it takes for the plant to mature or flower.
Kernel colour of the wheat:
Wheat kernel colour is determined by the expression of three independent pairs of alleles, each of which is responsible for a different colour. They demonstrate a diverse range of options. An intermediate red colour kernel is produced when the dark red wheat kernel (AABBCC) is crossed with the white wheat kernel (aabbcc), resulting in the F1 generation of wheat (AaBbCc). When the F1 generation is crossed with the F2 generation, the F2 generation has 63 red kernel plants with various shades of red and one white kernel.
Effect of environment on Polygenic Inheritance
It has been demonstrated that individuals may have genetic potential or vulnerability, but that environmental conditions influence the expression of a genotype in identical twins raised in two different environments.Examples:
- Diet and general health have a significant impact on height.
- The colour of a Hydrangea’s flower, as well as the colour of the shrub itself, is determined by the amount of aluminium present in the soil.
- The effect of temperature on the skin of Himalayan rabbits.
Conclusion
Many traits and phenotypic characteristics present in plants and animals, such as height, skin pigmentation, hair and eye colour, as well as milk and egg production, are inherited through a large number of alleles present in a variety of loci across the genome. Polygenic inheritance is the term used to describe this. If we look at the traits of height and skin pigmentation in humans, we will find that there are many different variations of these two characteristics. We are unable to divide people into simple categories such as ‘tall’ and short in terms of height or ‘dark’ and ‘light’ in terms of skin colour. As a result of the fact that these traits are controlled by multiple genes, we observe continuous variation for both of them. At least 400 genes regulate the trait of height and are responsible for the variation in height that exists within a population, according to some estimates.