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Heredity and variation: NEET MCQs with answers

111 questions on this topic of Genetics and Evolution (NEET 2027 syllabus). Here are 12; tap one to see its answer and explanation.

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easy

1. In 1900, Mendel's work was independently rediscovered by three scientists. Which of the following was NOT one of them?

  1. Hugo de Vries
  2. Thomas Hunt Morgan
  3. Carl Correns
  4. Erich von Tschermak
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Answer: (B) Thomas Hunt Morgan

de Vries, Correns and von Tschermak independently rediscovered Mendel's results in 1900. Morgan later worked on linkage in Drosophila.

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2. Assuming independent assortment, find the number of different genotypes in the F₂ of a cross between two AaBbCcDd individuals.

  1. 16
  2. 256
  3. 81
  4. 8
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Answer: (C) 81

With 4 heterozygous gene pairs: gametes = 2⁴ = 16, F₂ genotypes = 3⁴ = 81, F₂ phenotypes = 2⁴ = 16.

hard

3. In pea seeds, BB gives large starch grains and round seeds, bb gives small grains and wrinkled seeds, and Bb gives round seeds with intermediate-size grains. This shows that:

  1. B is always completely dominant
  2. The gene shows co-dominance for seed shape
  3. Starch synthesis is not genetic
  4. Dominance depends on the phenotype examined (seed shape vs starch grain size)
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Answer: (D) Dominance depends on the phenotype examined (seed shape vs starch grain size)

For seed shape, B is dominant (Bb seeds are round). For starch grain size, Bb is intermediate (incomplete dominance). Dominance is not an autonomous feature of a gene; it depends on the gene product and the phenotype chosen.

NCERT Class 12

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4. Assuming independent assortment, find the number of different phenotypes in the F₂ of a cross between two AaBbCc individuals (complete dominance).

  1. 8
  2. 6
  3. 27
  4. 64
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Answer: (A) 8

With 3 heterozygous gene pairs: gametes = 2³ = 8, F₂ genotypes = 3³ = 27, F₂ phenotypes = 2³ = 8.

easy

5. Gynaecomastia is a characteristic clinical feature observed in individuals suffering from:

  1. Turner's syndrome
  2. Down's syndrome
  3. Cri-du-chat syndrome
  4. Klinefelter's syndrome
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Answer: (D) Klinefelter's syndrome

Individuals with Klinefelter's syndrome (47, XXY) possess overall masculine development, but feminine traits such as gynaecomastia (development of breasts) are often expressed, and the individuals are sterile.

hard

6. In Morgan's crosses, the genes for white eye and yellow body showed only 1.3 per cent recombination, whereas white eye and miniature wing showed 37.2 per cent. This indicates that:

  1. White and miniature genes are closer together than white and yellow genes
  2. White and yellow genes are more tightly linked than white and miniature genes
  3. All three genes assort independently
  4. The genes are on different chromosomes
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Answer: (B) White and yellow genes are more tightly linked than white and miniature genes

Low recombination means genes are close and tightly linked. Sturtevant used such recombination frequencies to map the relative positions of genes.

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7. The physical expression of a genotype is called its:

  1. Allele
  2. Karyotype
  3. Genome
  4. Phenotype
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Answer: (D) Phenotype

Phenotype is the observable character (e.g. tall), while genotype is the genetic make-up (e.g. TT or Tt).

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8. Colour blindness is due to a defect in either the red or the green cone of the eye. It occurs in about:

  1. Equal frequencies in males and females
  2. 8 per cent of females and 0.4 per cent of males
  3. 8 per cent of males and 0.4 per cent of females
  4. 50 per cent of males
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Answer: (C) 8 per cent of males and 0.4 per cent of females

The gene is sex-linked recessive on the X chromosome, so it affects about 8 per cent of males but only about 0.4 per cent of females.

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9. The terms linkage and recombination were coined by Morgan. Linkage describes:

  1. Generation of non-parental gene combinations
  2. Crossing between two species
  3. Mutation of a gene
  4. The physical association of genes on a chromosome
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Answer: (D) The physical association of genes on a chromosome

Morgan used linkage for the physical association of genes on a chromosome, and recombination for the generation of non-parental gene combinations.

NCERT Class 12

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10. Assuming independent assortment, find the number of genetically different gametes produced by an individual of genotype Aa.

  1. 1
  2. 4
  3. 2
  4. 3
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Answer: (C) 2

With 1 heterozygous gene pair: gametes = 2¹ = 2, F₂ genotypes = 3¹ = 3, F₂ phenotypes = 2¹ = 2.

hard

11. Assertion (A): In a cross between pea plants heterozygous for round seeds (Bb), the seeds are round, yet their starch grains are of intermediate size. Reason (R): Dominance is not an autonomous feature of a gene; it depends on the phenotype chosen for examination. Choose the correct option.

  1. Both A and R are true and R is the correct explanation of A
  2. Both A and R are true but R is not the correct explanation of A
  3. A is true but R is false
  4. A is false but R is true
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Answer: (A) Both A and R are true and R is the correct explanation of A

For seed shape B is completely dominant (round), but for starch-grain size Bb is intermediate. This shows dominance depends on the character examined, which is exactly what R states.

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12. Sickle-cell anaemia is inherited as:

  1. An autosomal dominant trait
  2. A sex-linked recessive trait
  3. An autosomal recessive trait
  4. A Y-linked trait
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Answer: (C) An autosomal recessive trait

The disease shows only in Hb^S Hb^S homozygotes; heterozygotes (Hb^A Hb^S) are apparently unaffected carriers, so it is autosome-linked recessive.

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