Pleiotropy vs Polygenic Inheritance: Easy Difference for NEET
Biology · Principles of Inheritance and Variation · NEET
In pleiotropy, ONE gene affects MANY traits at once. The best NEET example is phenylketonuria, where one faulty gene causes mental problems and less hair and skin colour. In polygenic inheritance, MANY genes together control ONE trait, like human skin colour, which shows a smooth range of shades. Memory hook: "Pleiotropy = one-to-many, Polygenic = many-to-one." They are exact mirror images.
At a glance
Direction
One gene affects many traits
Many genes affect one trait
Number relation
One-to-many
Many-to-one
NCERT example
Phenylketonuria
Human skin colour
Phenotype pattern
Several distinct effects from one gene
Continuous gradient (additive)
Environment role
Not the main point
Also influences the trait
Inheritance type
Single-gene based
Non-Mendelian (NEET 2025)
Pleiotropy: one gene (phenylketonuria) causes many traits. Polygenic: many genes add up to control one trait (skin colour) as a smooth gradient.
Your doubts, answered
What is the simplest difference between pleiotropy and polygenic inheritance?
Just count the genes and the traits. Pleiotropy is ONE gene changing MANY traits (one-to-many). Polygenic inheritance is MANY genes controlling ONE trait (many-to-one). They are opposite directions, so if you remember one, you automatically know the other.
Is human skin colour pleiotropy or polygenic inheritance?
Skin colour is POLYGENIC inheritance. NCERT says it is controlled by three or more genes (like A, B, C) whose effects ADD UP, so you see a smooth gradient of shades, not just 'dark' or 'light'. This is the fixed NEET answer, so never match skin colour with pleiotropy.
Why is phenylketonuria an example of pleiotropy and not a disorder question?
Phenylketonuria comes from a mutation in ONE gene that makes the enzyme phenylalanine hydroxylase. That single faulty gene causes MANY effects at once: mental retardation plus reduced hair and skin pigmentation. Because one gene gives many phenotypes, NCERT uses it as the classic example of pleiotropy.
How is pleiotropy different from multiple alleles?
Do not mix these. Multiple alleles means one gene has more than two forms in the population (like IA, IB, i for blood group), but it still controls ONE trait. Pleiotropy means one gene controls MANY traits. Different words, different meaning.
Does polygenic inheritance follow Mendel's laws?
No. NEET 2025 confirmed polygenic traits follow a NON-Mendelian pattern. The reason: many genes act together, their effects are additive, and the environment also affects the result, so you get a continuous range instead of neat Mendelian ratios.
Why does polygenic inheritance give a continuous range of phenotypes?
Because each dominant allele adds a small equal amount to the trait. In skin colour, AABBCC is darkest and aabbcc is lightest, and every mix in between gives a slightly different shade. Adding effects of many genes plus environment creates a smooth gradient, not distinct classes.
⚠️ The NEET trap ✗ Matching Pleiotropy with human skin colour and Polygenic inheritance with phenylketonuria. ✓ Pleiotropy = phenylketonuria (one gene, many traits); Polygenic inheritance = human skin colour (many genes, one trait). 🧠 The trap swaps the two examples. Fix the pair in your head: skin colour is MANY genes (polygenic), phenylketonuria is ONE gene (pleiotropy). NEET reused this exact match in 2016 and 2026.
Real NEET questions
NEET 2026
Match List I with List II:
List-I: A. Incomplete dominance B. Co-dominance C. Pleiotropy D. Polygenic inheritance
List-II: I. Human skin colour II. Inheritance of flower colour in Antirrhinum sp. III. Phenylketonuria disease in humans IV. ABO blood groups
Choose the correct answer:
A · A-II, B-IV, C-III, D-I ✓
B · A-I, B-III, C-II, D-IV
C · A-I, B-IV, C-III, D-II
D · A-II, B-I, C-III, D-IV
Solution: Pleiotropy (C) is one gene with many effects, shown by phenylketonuria (III). Polygenic inheritance (D) is many genes controlling one trait, shown by human skin colour (I). Incomplete dominance (A) = Antirrhinum flower colour (II) and co-dominance (B) = ABO blood groups (IV). So the answer is A-II, B-IV, C-III, D-I, option (A).
NEET 2016
Match the following:
Column I: (a) Dominance (b) Codominance (c) Pleiotropy (d) Polygenic inheritance
Column II: (i) Many genes govern a single character (ii) In a heterozygous organism only one allele expresses itself (iii) In a heterozygous organism both alleles express themselves fully (iv) A single gene influences many characters
A · (a)-(ii), (b)-(i), (c)-(iv), (d)-(iii)
B · (a)-(ii), (b)-(iii), (c)-(iv), (d)-(i) ✓
C · (a)-(iv), (b)-(i), (c)-(ii), (d)-(iii)
D · (a)-(iv), (b)-(iii), (c)-(i), (d)-(ii)
Solution: Pleiotropy (c) is 'a single gene influences many characters' (iv). Polygenic inheritance (d) is 'many genes govern a single character' (i). Dominance (a) means only one allele expresses in a heterozygote (ii), and co-dominance (b) means both alleles express fully (iii). This gives (a)-(ii), (b)-(iii), (c)-(iv), (d)-(i), option (B).
NEET 2023
The phenomenon of pleiotropism refers to
A · presence of several alleles of a single gene controlling a single crossover
B · presence of two alleles, each of the two genes controlling a single trait
C · a single gene affecting multiple phenotypic expression ✓
D · more than two genes affecting a single character
Solution: Pleiotropy is when a single gene shows multiple phenotypic effects, usually by acting on several steps of a metabolic pathway (example: phenylketonuria). Option (D), 'more than two genes affecting a single character', describes POLYGENIC inheritance, not pleiotropy, so option (C) is correct.
Solved Principles of Inheritance and Variation NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
What is the one-line difference between pleiotropy and polygenic inheritance?
Pleiotropy = one gene, many traits (one-to-many). Polygenic inheritance = many genes, one trait (many-to-one). They are exact opposites.
What is the NCERT example of pleiotropy?
Phenylketonuria in humans. One mutated gene for the enzyme phenylalanine hydroxylase causes several effects: mental retardation and reduced hair and skin pigmentation.
What is the NCERT example of polygenic inheritance?
Human skin colour. Three or more genes act together with additive effects, plus the environment, giving a continuous range of shades.
Which one is non-Mendelian?
Polygenic inheritance follows a non-Mendelian pattern (confirmed in NEET 2025) because effects add up and the environment plays a role, giving a continuous gradient instead of clear ratios.
Can a trait be both polygenic and pleiotropic?
For NEET, keep them separate and use the fixed NCERT examples. Focus on the direction: count genes and traits to decide which term applies.
