Galton in 1883 suggested that many instances of continuous variation are heritable like height, mental capabilities.
The character is determined by more than one gene each with the same but cumulative phenotypic effect.
Quantitative characters like plant height, yield of crops (size, shape and number of seeds and fruits per plant), intelligence in human beings and milk yield in animals determined by many genes in cumulative.
Skin colour determine by 3 genes (6 allels)
(i) Few individuals fall into parental categories;
(ii) The expression level of the phenotype is dependent upon the number of contributive alleles and is hence more quantitative.
Polygenic inheritance also shows by kernel colour in wheat and inheritance of cob length in maize. It is generally believed that during evolution there was duplication of chromosome or chromosome parts thereby leading to multiple copies of the same gene. A large number of characters are controlled by polygenes in which alleles contribute additively to a phenotype. This results in polygenic inheritance.
