Polygenic Inheritance MCQ - Practice Questions & Answers

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Polygenic Inheritance is considered one the most difficult concept.
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Polygenic Inheritance

Mendel’s studies mainly described those traits that have distinct alternate forms such as flower colour which are either purple or white.
However, there are some human characteristics, such as height, eye color, and hair color, that don't come in just a few distinct forms.
Instead, they vary in small gradations, forming a spectrum or continuum of possible phenotypes.
Features like these are called quantitative characters, and they’re typically controlled by multiple genes (often, many genes), each of which contributes to the overall phenotype.
For example, in humans we don’t just have tall or short people as two distinct alternatives but a whole range of possible heights.
Besides the involvement of multiple genes polygenic inheritance also takes into account the influence of environment.
Human skin colour is another classic example for this.
In a polygenic trait the phenotype reflects the contribution of each allele, i.e., the effect of each allele is additive.
To understand this better let us assume that three genes A, B, C control skin colour in humans with the dominant forms A, B and C responsible for dark skin colour and the recessive forms a, b and c for light skin colour.
The genotype with all the dominant alleles (AABBCC) will have the darkest skin colour and that with all the recessive alleles (aabbcc) will have the lightest skin colour.
As expected the genotype with three dominant alleles and three recessive alleles will have an intermediate skin colour.
In this manner the number of each type of alleles in the genotype would determine the darkness or lightness of the skin in an individual.