Polygenic inheritance explained

Many traits and phenotypic characters present in plants and animals such as height, skin pigmentation, hair and eye colour, milk and egg production are inherited through many alleles present in different loci. This is known as polygenic inheritance.
If we take an example of height or skin pigmentation in humans, we find many different forms of the two traits. We can’t categorise people in just two categories like ‘tall’ and ‘short’ for height or ‘dark’ and ‘light’ for the skin colour. We find continuous variation for both these traits because these traits are controlled by multiple genes. There are as many as 400 genes that control the trait of height and are responsible for variation in height present in the population.

Polygenic inheritance is also known as multiple gene inheritance or multiple factor inheritance.

Polygenic Inheritance characteristics
Polygene refers to a gene that exerts a slight effect on a phenotype along with other genes
Effect of a single gene is too small, so it is difficult to detect
Multiple genes produce an equal effect
Each allele has a cumulative or additive effect
Polygenic inheritance differs from multiple alleles, as in multiple alleles, three or more alleles are present in the same locus of which any two alleles are present in an organism, e.g. ABO blood group system, which is controlled by three alleles
There is no epistasis involved, i.e. masking of the expression of an allele of the different locus
There is no linkage or dominance, rather there exist contributing and non-contributing alleles, which are known as active or null alleles respectively
Polygenic inheritance is characterised by the continuous variation of the phenotype of a trait
The polygenic inheritance pattern is complex. It is difficult to predict phenotype
The statistical analysis can give the estimate of population parameters