Polygenic traits follow a inheritance pattern.
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. Show
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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 Definition
Polygenic inheritance is also known as multiple gene inheritance or multiple factor inheritance. Polygenic Inheritance characteristics
Polygenic Inheritance ExamplesPolygenic Inheritance in Humans There are many traits in humans, which show polygenic inheritance, e.g. skin and hair colour, height, eye colour, the risk for diseases and resistance, intelligence, blood pressure, bipolar disorder, autism, longevity, etc. Brief description of some of the traits:
Punnett square showing F2 generation offsprings continuous variation From light to dark→
Polygenic Inheritance in Plants Polygenic inheritance in plants includes the colour and shape of the stem, pollen, flower, yield, oil content, size of a seed, time to mature or flower, etc. Brief description of some of the traits:
F2 1615201561Dark redModerate RedRedIntermediate redLight redVery light redWhite 63 Red (many shades):1 (white)
Effect of environment on Polygenic InheritanceThe expression of polygenes is greatly influenced by environmental conditions. The genotype sets the range for a quantitative trait, but the environmental conditions decide the phenotype within its genetic limits. Genes function differently in different environmental conditions. Environment regulates the activity of certain genes and sets them on or off. The range of phenotype possible under the different environmental conditions from the same genotype is termed as ‘norm of reaction’. The norm of the reaction is narrow for certain genotypes and broad for some genotypes, e.g. genotypes involved in human height have a very broad norm of reaction. Identical twins raised in two different environments show that individuals may have genetic potential or vulnerability, but environmental conditions influence the expression of genotype. Human characters such as intelligence, depression, height, skin colour, schizophrenia show the effect of the environment on gene expression. Phenotypic expression is dependent on both nature and nurture. Examples:
Frequently Asked QuestionsPolygenic inheritance refers to the inheritance of a trait governed by more than one genes. Generally, three or more genes govern the inheritance of polygenic traits. Multiple independent genes have an additive or similar effect on a single quantitative trait. In polygenic inheritance, each allele has a cumulative or additive effect on the phenotype thus generating continuous variation, e.g. skin pigmentation, height, etc. Three examples of polygenic traits in humans are height, skin colour and eye colour. These traits are governed by multiple genes. ABO blood type is an example of multiple allelism, where a single gene has three different alleles or variants (in the same locus) and an individual contains any of the two alleles. It is different from polygenic inheritance. Gene I has 3 alleles IA, IB and i. The combination of two allele pair decides the blood type. Yes, eye colour is a polygenic trait. There are two major eye colour genes, OCA2 and HERC2, which are present on chromosome 15. Other than these, there are more than 13 genes identified that determine the expression of the phenotype (colour of eye). At least 9 colours of eye are recognised in humans. |