Polygenic Inheritance of Skin Pigmentation

Multiple-gene inheritance (also known as polygenic inheritance, multigenic inheritance, or quantitative inheritance) is a type of non-Mendelian inheritance that differs from a single-gene inheritance, which is the fundamental concept of Mendelian inheritance. An individual polygene 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). 

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

Many human characteristics, such as skin and hair colour, height, eye colour, the likelihood of developing diseases and developing resistance, intelligence, blood pressure, bipolar disorder, autism, longevity, and many others, can be traced back to polygenic inheritance.

The following is a brief description of some of the characteristics:

Pigmentation of The Skin

Skin pigmentation is inherited through a polygenic inheritance pattern. A single trait is inherited through the contribution of approximately 60 loci. Take, for example, a pair of alleles from three different and unrelated loci, denoted by the letters A and a, B and b, and C and c. The allele for dark skin colour represented by the capital letters is an incompletely dominant allele. The greater the number of capital letters, the darker the skin colour is represented, and the smaller the number of capital letters, the lighter the skin colour is represented. Genetically parents with genotypes AABBCC and aabbcc will produce offspring of intermediate colour in the F1 generation, which is genetically identical to the genotype AaBbCc. When two triple heterozygotes (AaBbCc x AaBbCc) mate, the resulting F2 generation will have a range of phenotypes ranging from very dark to very light in the ratio 1:6:15:20:15:6:1 from very dark to very light.

Height

The phenotype is determined by approximately 400 genes, and the environment has a significant impact on the expression of these genes.

Colour of Eyes

Polygenes are involved in determining the colour of one’s eyes. Humans can tell the difference between at least nine different eye colours. Eye colour is influenced by two major genes, as well as 14 other genes that influence the expression of the phenotype. A different number of alleles must be present for each colour to be achieved. It has been discovered that these are X-linked.

Plant Polygenic Inheritance

The colour and shape of the stem, pollen, flower, yield, oil content, seed size, and the length of time it takes for the plant to mature or flower are all polygenic traits in plants.

Wheat’s Kernel Colour

The expression of three independent pairs of alleles, each of which is responsible for a different colour, determines the colour of wheat kernels. They show a wide range of possibilities. When the dark red wheat kernel (AABBCC) is crossed with the white wheat kernel (aabbcc), an intermediate red colour kernel is produced, resulting in the F1 generation of wheat (AaBbCc). When the F1 and F2 generations are crossed, the F2 generation produces 63 red kernel plants in various shades of red and one white kernel.

Conclusion

Many plant and animal traits and phenotypic characteristics, such as height, skin pigmentation, hair and eye colour, as well as milk and egg production, are inherited through a large number of alleles found in a variety of loci across the genome. The term “polygenic inheritance” is used to describe this. When we look at the human traits of height and skin pigmentation, we can see that there are many different variations of these two traits. We can’t categorise people into simple groups like ‘tall’ and short in terms of height or ‘dark’ and ‘light’ in terms of skin colour. We see continuous variation for both of these traits as a result of the fact that they are controlled by multiple genes. According to some estimates, at least 400 genes regulate the trait of height and are responsible for the variation in height that exists within a population.