Genetics – Pleiotropy and Polygenic Inheritance: NEET MCQs with Answers

15 free questions on Genetics – Pleiotropy and Polygenic Inheritance for NEET (UG), starting with previous-year NEET and AIPMT questions. Try each one, then tap Show answer for the answer and a short explanation.

Syllabus covered: Pleiotropy and Polygenic Inheritance: Deviations from Mendelism, Incomplete dominance, Co-dominance, Multiple alleles and Inheritance of blood groups, Pleiotropy; Elementary idea of polygenic inheritance;

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Question 1

Previous-year question
Identify the wrong statement with reference to the gene 'I' that controls ABO blood groups. [NEET 2020]
  1. A person will have only two of the three alleles
  2. When IA and IB are present together, they express the same type of sugar
  3. The allele 'i' does not produce any sugar
  4. The gene (I) has three alleles
Show answer
Answer: (B) When IA and IB are present together, they express the same type of sugar
Explanation: IA and IB code for two different sugars, so an IAIB individual carries both antigen A and antigen B on the red cells. That is why the AB group is the classical example of co-dominance.

Question 2

Previous-year question
In Antirrhinum (snapdragon), a red flower was crossed with a white flower and pink flowers were obtained in the F1. When the pink flowers were selfed, the F2 showed white, red and pink flowers. Choose the incorrect statement. [NEET 2019]
  1. This experiment does not follow the principle of dominance
  2. Pink colour in the F1 is due to incomplete dominance
  3. The F2 ratio is 1/4 red : 2/4 pink : 1/4 white
  4. The law of segregation does not apply in this experiment
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Answer: (D) The law of segregation does not apply in this experiment
Explanation: The reappearance of the pure red and pure white parental phenotypes in the F2 proves that the alleles separated unchanged during gamete formation, so the law of segregation does hold. Only the principle of complete dominance is violated.

Question 3

Previous-year question
Which of the following pairs is wrongly matched? [NEET 2018]
  1. Starch synthesis in pea : Multiple alleles
  2. ABO blood grouping : Co-dominance
  3. T. H. Morgan : Linkage
  4. XO type sex determination : Grasshopper
Show answer
Answer: (A) Starch synthesis in pea : Multiple alleles
Explanation: Starch synthesis in pea is governed by a single gene B with two alleles, and the heterozygote Bb produces intermediate-sized starch grains — an example of incomplete dominance and pleiotropy, not of multiple alleles.

Question 4

Previous-year question
Which of the following characteristics represent 'inheritance of blood groups' in humans? A. Dominance, B. Co-dominance, C. Multiple alleles, D. Incomplete dominance, E. Polygenic inheritance. [NEET 2018]
  1. B, C and E
  2. A, B and C
  3. A, C and E
  4. B, D and E
Show answer
Answer: (B) A, B and C
Explanation: The ABO system involves three alleles at one locus (multiple alleles), IA and IB are both dominant over i (dominance), and together they show co-dominance. Incomplete dominance and polygenic inheritance are not involved.

Question 5

Previous-year question
The genotypes of a husband and wife are IAIB and IAi. Among the blood types of their children, how many different genotypes and phenotypes are possible? [NEET 2017]
  1. 3 genotypes; 4 phenotypes
  2. 4 genotypes; 3 phenotypes
  3. 4 genotypes; 4 phenotypes
  4. 3 genotypes; 3 phenotypes
Show answer
Answer: (B) 4 genotypes; 3 phenotypes
Explanation: The cross IAIB × IAi gives IAIA, IAi, IAIB and IBi — four genotypes. Since IAIA and IAi are both blood group A, only three phenotypes (A, AB and B) appear.

Question 6

Previous-year question
Match the terms in Column-I with their descriptions in Column-II. Column-I: (A) Dominance, (B) Codominance, (C) Pleiotropy, (D) Polygenic. 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 inheritance influences many characters. [NEET 2016]
  1. A–II, B–I, C–IV, D–III
  2. A–II, B–III, C–IV, D–I
  3. A–IV, B–I, C–II, D–III
  4. A–IV, B–III, C–I, D–II
Show answer
Answer: (B) A–II, B–III, C–IV, D–I
Explanation: Dominance means only one allele expresses in the heterozygote (II); codominance means both express fully (III); pleiotropy is one gene influencing many characters (IV); and polygenic inheritance is many genes governing a single character (I).

Question 7

Previous-year question
A pleiotropic gene [AIPMT 2015]
  1. Is a gene evolved during the Pliocene
  2. Controls a trait only in combination with another gene
  3. Controls multiple traits in an individual
  4. Is expressed only in primitive plants
Show answer
Answer: (C) Controls multiple traits in an individual
Explanation: A pleiotropic gene produces multiple phenotypic effects. In phenylketonuria, for example, a single mutant gene causes mental retardation together with reduced hair and skin pigmentation.
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Question 8

Previous-year question
A gene showing co-dominance has [AIPMT 2015]
  1. Alleles tightly linked on the same chromosome
  2. Alleles that are recessive to each other
  3. Both alleles independently expressed in the heterozygote
  4. One allele dominant over the other
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Answer: (C) Both alleles independently expressed in the heterozygote
Explanation: In co-dominance the heterozygote expresses the products of both alleles fully and independently, as seen in the AB blood group where both A and B antigens are present on the erythrocyte surface.

Question 9

Previous-year question
Multiple alleles are present [AIPMT 2015]
  1. At different loci on the same chromosome
  2. At the same locus of the chromosome
  3. On non-sister chromatids
  4. On different chromosomes
Show answer
Answer: (B) At the same locus of the chromosome
Explanation: Multiple alleles are three or more alternative forms of the same gene, and by definition they all occupy the identical locus on homologous chromosomes. Any one diploid individual therefore carries only two of them.

Question 10

Previous-year question
A person with blood group AB is considered a universal recipient because he has [AIPMT 2014]
  1. Both A and B antigens on the RBCs but no antibodies in the plasma
  2. Both A and B antibodies in the plasma
  3. No antigen on the RBCs and no antibody in the plasma
  4. Both A and B antigens in the plasma but no antibodies
Show answer
Answer: (A) Both A and B antigens on the RBCs but no antibodies in the plasma
Explanation: Group AB red cells carry both A and B antigens, and because the person does not make antibodies against his own antigens, the plasma contains neither anti-A nor anti-B. Hence blood of any ABO group can be received without agglutination.

Question 11

Previous-year question
Fruit colour in squash is an example of [AIPMT 2014]
  1. Recessive epistasis
  2. Dominant epistasis
  3. Complementary genes
  4. Inhibitory genes
Show answer
Answer: (B) Dominant epistasis
Explanation: In squash a dominant allele at one locus prevents the expression of the alleles of another locus, producing a modified F2 ratio of 12:3:1. This masking by a dominant allele is dominant epistasis.

Question 12

Previous-year question
When a single gene influences more than one traits, it is called [AIPMT 1998]
  1. pleiotropy
  2. epistasis
  3. pseudodominance
  4. None of these
Show answer
Answer: (A) pleiotropy
Explanation: Pleiotropy is the condition in which a single gene influences more than one trait. For example, the sickle-cell gene produces both anaemia and resistance to malaria.

Question 13

Previous-year question
A polygenic inheritance in human beings is [AIPMT 2007, 2006, 1999, 1993]
  1. skin colour
  2. phenylketonuria
  3. colour blindness
  4. sickle-cell anaemia
Show answer
Answer: (A) skin colour
Explanation: Human skin colour is a classic polygenic (quantitative) trait controlled by at least three separate gene pairs. The phenotype depends on the cumulative or additive effect of the contributing alleles, producing a continuous range of shades.

Question 14

Previous-year question
A pleiotropic gene [AIPMT 2015]
  1. is expressed only in primitive plants
  2. is a gene evolved during Pliocene
  3. controls a trait only in combination with another gene
  4. controls multiple traits in an individual
Show answer
Answer: (D) controls multiple traits in an individual
Explanation: A pleiotropic gene is one that controls several different traits in an individual. Phenylketonuria illustrates this, where mutation in the single gene coding for phenylalanine hydroxylase produces several distinct effects.

Question 15

Previous-year question
Match the terms in column I with their description in column II and choose the correct option. [NEET 2016, Phase I] Column I: A. Dominance, B. Codominance, C. Pleiotropy, D. Polygenic inheritance Column II: 1. Many genes govern a single character, 2. In a heterozygous organism only one allele expresses itself, 3. In a heterozygous organism both alleles express themselves fully, 4. A single gene influences many characters
  1. A-2, B-3, C-4, D-1
  2. A-4, B-1, C-2, D-3
  3. A-4, B-3, C-1, D-2
  4. A-2, B-1, C-4, D-3
Show answer
Answer: (A) A-2, B-3, C-4, D-1
Explanation: In dominance only one allele of the heterozygote is expressed (A–2); in codominance both alleles express fully (B–3); in pleiotropy a single gene influences many characters (C–4); and in polygenic inheritance many genes govern one character (D–1).

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