Q.Which one of the following is an example of polygenic inheritance ?
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Polygenic inheritance is the pattern in which several different genes, each typically with two or more alleles, act together in an additive way to determine a single trait, producing continuous (quantitative) variation rather than a small number of sharply distinct classes. Swedish geneticist H. Nilsson-Ehle gave the first experimental demonstration of this in 1909, using wheat kernel colour: crossing dark red (R1R1R2R2) with white (r1r1r2r2) wheat gave a medium-red F1, and the F2 generation showed kernel-colour intensity tracking directly with how many 'R' alleles (of either gene) a plant carried - each R allele adding a fixed increment of red pigment. Plotting individuals against colour intensity produces the characteristic bell-shaped curve of …
Skin colour in humans is the classic textbook example of polygenic inheritance, where several genes (each with a small, additive effect, historically estimated at 3-4 gene pairs) act together to produce a continuous range of skin-colour phenotypes, from very light to very dark, rather than the sharp either/or classes seen in single-gene traits. Pod shape in garden pea (inflated vs constricted) and flower colour in Mirabilis jalapa (red/pink/white, via incomplete dominance) are each controlled by a SINGLE g …
Human skin colour, controlled additively by several genes to give a continuous range of shades, is the classic example of polygenic inheritance among the options given.
Working
Polygenic inheritance occurs when a single phenotypic trait is controlled not by one gene but by several genes acting together, each contributing a small, additive effect, so that the trait shows continuous (quantitative) variation across a whole range of intermediate phenotypes rather than a few discrete classes -- the population distribution for such a trait typically approximates a bell (normal) curve. Human skin colour is the standard textbook illustration: multiple gene pairs (classically estimated as 3 or 4) each add or subtract pigment (melanin) in an additive fashion, producing the wide, continuous spectrum of human skin shades seen across populations.
By contrast:
- Pod shape in garden pea (inflated dominant over constricted) is a simple monohybrid (single-gene) Mendelian trait, not polygenic. …
- CBSE 2026Set ANNUAL1 markMCQQ.Which one of the following is an example of polygenic inheritance ?(a) Pod shape in garden pea(b) Flower colour in Mirabilis jalapa(c) Skin colour in humans(d) Production of male honeybee
›Reveal solutionSolution
Human skin colour, controlled additively by multiple genes and showing continuous variation, is the example of polygenic inheritance among the four options.
Working
Polygenic inheritance refers to traits controlled by two or more genes (loci) acting together in an additive fashion, so that the phenotype shows continuous (quantitative) variation across a range, rather than falling into a small number of sharply distinct classes, and is often also influenced by environmental factors. Checking each option: pod shape in garden pea (inflated vs constricted) is one of Mendel's seven classic traits, governed by a single gene showing simple dominant-recessive inheritance -- not polygenic. Flower colour in Mirabilis jalapa (red x white giving pink) is the classic textbook example of incomplete dominance, still controlled by a single gene with two alleles that blend in the heterozygote -- again not polygenic. Production of male honeybees is explained by haplodiploidy: unfertilised (haploid) eggs develop into males (drones), while fertilised (diploid) eggs develop into females …
- CBSE 2026Set SEM31 markMCQQ.Which of the following is not an example of Polygenic inheritance ?(a) Human skin colour(b) ABO blood group(c) Grain colour of wheat(d) Human body height
›Reveal solutionSolution
Polygenic inheritance = a trait controlled by many genes with additive effects (skin colour, wheat grain colour, height). ABO blood group is controlled by three alleles of ONE gene (multiple allelism), so it is not polygenic.
Polygenic (quantitative) inheritance involves several genes each adding a small, cumulative effect, producing continuous variation. Examples: human skin colour, grain (kernel) colour in wheat, and human height — all show a gradient of phenotypes.
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- CBSE 2025Set F1 markMCQQ.By which of the following means is the colour of skin determined in human being?(a) Quantitative(b) Multiple gene(c) Qualitative(d) All of these
›Reveal solutionSolution
Skin colour in humans is determined by several genes acting together — polygenic (multiple-gene) inheritance.
Skin colour is a classic example of polygenic (quantitative) inheritance, controlled by multiple genes (chiefly those governing melanin production). The combined effect of several genes produces a continuous range of skin shades from very light to very dark, rather than distinct categories.
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- CBSE 2025Set ANNUAL1 markQ.Skin colour of human is polygenic. Give reason.
›Reveal solutionSolution
Skin colour is polygenic because several genes, each with a small cumulative (additive) effect, jointly determine the total amount of melanin pigment, producing a continuous range of shades.
In polygenic inheritance, a phenotype is controlled by three or more genes, and the effect of each individual gene's alleles is small but additive — the more "effective" (pigment-producing) alleles an individual has, the more extreme the phenotype. Human skin colour is a classic example: it is governed by at least three genes (each with a dark and a light allele), and the cumulative dosage of the dark alleles across all these genes determines how much melanin is produced. Because there are several genes each contributing incrementally, the population shows a continuous gradation of skin colours (from very fair to very dark) rather than a few sharply distinct classes, as would be seen with a simple monogenic (sin …
- CBSE 2025Set ANNUAL1 markMCQQ.Which one of the following is an example of polygenic inheritance ?(a) Pod shape in Garden Pea(b) Flower colour in Mirabilis jalapa(c) Skin colour in humans(d) Production of male honey bee
›Reveal solutionSolution
Human skin colour, controlled additively by several genes to give a continuous range of shades, is the classic example of polygenic inheritance among the options given.
Working
Polygenic inheritance occurs when a single phenotypic trait is controlled not by one gene but by several genes acting together, each contributing a small, additive effect, so that the trait shows continuous (quantitative) variation across a whole range of intermediate phenotypes rather than a few discrete classes -- the population distribution for such a trait typically approximates a bell (normal) curve. Human skin colour is the standard textbook illustration: multiple gene pairs (classically estimated as 3 or 4) each add or subtract pigment (melanin) in an additive fashion, producing the wide, continuous spectrum of human skin shades seen across populations.
By contrast:
- Pod shape in garden pea (inflated dominant over constricted) is a simple monohybrid (single-gene) Mendelian trait, not polygenic. …
- CBSE 2024Set ANNUAL1 markMCQQ.Inheritance of skin colour in human is an example of -(i) epistasis(ii) codominance(iii) polygenic inheritance(iv) chromosomal aberration
›Reveal solutionSolution
Skin colour results from the additive, cumulative effect of several genes, so it shows continuous (quantitative) variation — this is polygenic inheritance.
Unlike traits controlled by a single gene, human skin colour is governed by at least three genes, each with an additive (non-dominant, cumulative) effect. The more 'dark alleles' an individual inherits, the darker the skin tone, and the fewer, the lighter — producing a continuous gradation of colour in the population rather than distinct classes. Th …
- CBSE 2023Set 57/3/11 markMCQQ.For Questions number 13 to 16, two statements are given — one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to these questions from the codes (a), (b),(c) and(d) as given below.(a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).(b) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).(c) Assertion (A) is true, but Reason (R) is false.(d) Assertion (A) is false, but Reason (R) is true. Assertion (A) : In humans the genotype with all the dominant alleles (AABBCC) will have the darkest skin colour. Reason (R) : In a polygenic trait, phenotype reflects the contribution of each allele.
›Reveal solutionSolution
The key idea is that skin colour in humans is a polygenic trait where each dominant allele adds pigment. The darkest skin requires all dominant alleles, so Assertion (A) is true; Reason (R) correctly explains that phenotype reflects the contribution of each allele, making both true and (R) the correct explanation.
Concept and intuition:
Skin colour in humans is not controlled by a single gene with simple dominance. Instead, it is a polygenic trait — influenced by multiple genes (here, three genes: A, B, C). Each dominant allele (A, B, C) contributes a unit of melanin (dark pigment), while each recessive allele (a, b, c) contributes less. The total number of dominant alleles determines the skin shade: more dominant alleles → darker skin. The genotype AABBCC has six dominant alleles (the maximum possible), so it gives the darkest skin. Reason (R) states that in a polygenic trait, the phenotype reflects the additive contribution of each allele — which is exactly why AABBCC is darkest. So (R) correctly explains (A).
Step-by-step reasoning:
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Identify the trait type:
Skin colour in humans is a classic example of polygenic inheritance (also called quantitative inheritance). Unlike Mendelian traits with clear dominant/recessive pairs, polygenic traits show continuous variation (e.g., light to dark skin). The phenotype is determined by the total number of dominant alleles across multiple genes.
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Understand the additive model:
For three genes (A/a, B/b, C/c), each dominant allele adds a fixed amount of pigment. So:
- Genotype
aabbcc(0 dominant alleles) → lightest skin. - Genotype
AABBCC(6 dominant alleles) → darkest skin. - Intermediate numbers (1 to 5 dominant alleles) produce intermediate shades.
- Genotype
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Evaluate Assertion (A):
"In humans the genotype with all the dominant alleles (AABBCC) will have the darkest skin colour."
This is true — because it has the maximum possible number of dominant alleles (6), hence the maximum pigment.
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Evaluate Reason (R):
"In a polygenic trait, phenotype reflects the contribution of each allele."
This is true — the additive effect of each dominant allele is exactly what produces the range of skin colours. The phenotype is a sum of individual allele contributions. …
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- CBSE 2019Set ANNUAL1 markMCQQ.Example of Polygenic Inheritance is(a) human skin colour(b) sickle cell anaemia(c) ABO group(d) cystic fibrosis
›Reveal solutionSolution
Polygenic inheritance = a trait controlled by many genes; human skin colour is the standard example — the answer is (a).
Polygenic inheritance is the control of a single character by two or more genes, where each contributing (additive) allele adds a small quantitative effect, producing a continuous range of phenotypes.
- (a) Human skin colour — governed by multiple genes (e.g. three or more) whose additive alleles determine the amount of melanin, giving a whole gradient from very dark to very fair. This is the textbook example of polygenic inheritance. ✓ …
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