Chapter 5: Principles of Inheritance and Variation – MCQs with Answers & Explanations

CBSE Class 12 Biology MCQs with Answers & Explanations (NCERT): Principles of Inheritance and Variation

Course & Examination Details

• Course: CBSE Class 12 Biology
• Unit: Unit II – Genetics and Evolution
• Chapter: Chapter 5 – Principles of Inheritance and Variation
• Prescribed Textbook: NCERT Biology Class XII
• Examination: CBSE Class 12 Board Examination
• Question Type: Multiple Choice Questions (MCQs)
• Coverage: Conceptual, application-based, competency-oriented

Section A: Mendel’s Experiments and Laws of Inheritance

Q1. Who is regarded as the father of genetics?

A. Darwin
B. Lamarck
C. Gregor Mendel
D. Morgan

Correct Answer: C
Explanation: Mendel established basic laws of inheritance through systematic experiments on pea plants, laying the foundation of genetics.

Q2. Which plant did Mendel use for his experiments?

A. Maize
B. Wheat
C. Sunflower
D. Pea

Correct Answer: D
Explanation: Pea plants had clear contrasting traits, short life cycle, and were suitable for controlled pollination.

Q3. The Law of Dominance states that:

A. Both alleles express equally
B. One allele masks the other
C. Alleles blend together
D. Traits skip generations

Correct Answer: B
Explanation: In a heterozygote, the dominant allele expresses itself while the recessive allele remains masked.

Q4. The Law of Segregation is also known as:

A. Law of linkage
B. Law of purity of gametes
C. Law of recombination
D. Law of variation

Correct Answer: B
Explanation: Alleles separate during gamete formation, ensuring gametes are genetically pure.

Q5. Which Mendelian law is proved by a dihybrid cross?

A. Dominance
B. Segregation
C. Independent assortment
D. Linkage

Correct Answer: C
Explanation: A dihybrid cross shows that alleles of different genes assort independently.

Section B: Monohybrid and Dihybrid Crosses

Q6. The phenotypic ratio in a monohybrid cross is:

A. 1:2:1
B. 9:3:3:1
C. 3:1
D. 1:1

Correct Answer: C
Explanation: Dominant and recessive traits segregate in a 3:1 ratio in the F₂ generation.

Q7. The genotypic ratio in a monohybrid cross is:

A. 3:1
B. 1:2:1
C. 9:3:3:1
D. 1:1

Correct Answer: B
Explanation: F₂ generation shows TT:Tt:tt in the ratio 1:2:1.

Q8. A test cross is performed to determine:

A. Phenotype
B. Dominant trait
C. Genotype
D. Mutation

Correct Answer: C
Explanation: A test cross reveals whether an individual with dominant phenotype is homozygous or heterozygous.

Q9. Which ratio is obtained in a dihybrid cross?

A. 3:1
B. 1:2:1
C. 9:3:3:1
D. 1:1:1:1

Correct Answer: C
Explanation: Independent assortment of two gene pairs produces four phenotypes in 9:3:3:1 ratio.

Q10. Independent assortment occurs when genes are:

A. Linked
B. On same chromosome
C. Close together
D. On different chromosomes

Correct Answer: D
Explanation: Genes on different chromosomes assort independently during meiosis.

Section C: Deviations from Mendelian Inheritance

Q11. In incomplete dominance, the heterozygote shows:

A. Dominant phenotype
B. Recessive phenotype
C. Intermediate phenotype
D. No phenotype

Correct Answer: C
Explanation: Neither allele is completely dominant, producing an intermediate expression.

Q12. Example of incomplete dominance is seen in:

A. ABO blood group
B. Mirabilis jalapa
C. Pea plant height
D. Human eye colour

Correct Answer: B
Explanation: Red × white flowers produce pink offspring.

Q13. Codominance is best shown by:

A. Flower colour
B. Skin colour
C. ABO blood group
D. Height

Correct Answer: C
Explanation: Both IA and IB alleles express equally in AB blood group.

Q14. Phenotypic ratio in incomplete dominance is:

A. 3:1
B. 9:3:3:1
C. 1:1
D. 1:2:1

Correct Answer: D
Explanation: Each genotype has a distinct phenotype.

Q15. Multiple alleles are present at the:

A. Individual level
B. Gamete level
C. Population level
D. Cellular level

Correct Answer: C
Explanation: More than two alleles exist in a population, but individuals carry only two.

Section D: Multiple Alleles and Pleiotropy

Q16. How many alleles control the ABO blood group system?

A. Two
B. Three
C. Four
D. One

Correct Answer: B
Explanation: IA, IB, and i alleles control ABO blood groups.

Q17. Pleiotropy refers to:

A. One gene, many traits
B. Many genes, one trait
C. One chromosome, many genes
D. Many alleles, one gene

Correct Answer: A
Explanation: A single gene influences multiple phenotypic traits.

Q18. Phenylketonuria is an example of:

A. Codominance
B. Linkage
C. Pleiotropy
D. Mutation only

Correct Answer: C
Explanation: One gene mutation causes multiple effects.

Q19. Which increases genetic diversity in a population?

A. Homozygosity
B. Multiple alleles
C. Dominance
D. Purity of gametes

Correct Answer: B
Explanation: Multiple alleles create more phenotypic variations.

Q20. ABO blood group system demonstrates:

A. Incomplete dominance
B. Linkage
C. Codominance and multiple alleles
D. Pleiotropy only

Correct Answer: C
Explanation: It shows both codominance (IA, IB) and multiple alleles.

Section E: Chromosomal Theory, Linkage & Recombination

Q21. Chromosomal theory of inheritance was proposed by:

A. Mendel
B. Morgan
C. Sutton and Boveri
D. Watson and Crick

Correct Answer: C
Explanation: They correlated Mendelian laws with chromosome behaviour.

Q22. Genes located close together show:

A. Independent assortment
B. Linkage
C. Mutation
D. Segregation

Correct Answer: B
Explanation: Linked genes are inherited together.

Q23. Recombination occurs due to:

A. Mutation
B. Independent assortment
C. Crossing over
D. Fertilisation

Correct Answer: C
Explanation: Exchange of genetic material occurs during crossing over.

Q24. Recombination occurs during:

A. Prophase I
B. Metaphase I
C. Anaphase I
D. Telophase I

Correct Answer: A
Explanation: Crossing over takes place in prophase I of meiosis.

Q25. Low recombination frequency indicates genes are:

A. Far apart
B. On different chromosomes
C. Closely linked
D. Independent

Correct Answer: C
Explanation: Closely placed genes recombine less frequently.

Section F: Sex Determination Mechanisms

Q26. Human sex determination system is:

A. XX–XO
B. ZW–ZZ
C. Haplodiploid
D. XX–XY

Correct Answer: D
Explanation: Females are XX and males are XY.

Q27. Who is heterogametic in humans?

A. Female
B. Male
C. Both
D. None

Correct Answer: B
Explanation: Males produce X and Y bearing sperms.

Q28. In birds, females are:

A. XX
B. XO
C. ZW
D. ZZ

Correct Answer: C
Explanation: Birds show ZW–ZZ sex determination.

Q29. Haplodiploidy is seen in:

A. Humans
B. Birds
C. Honeybees
D. Frogs

Correct Answer: C
Explanation: Males are haploid and females are diploid.

Q30. Sex of the human child is determined by:

A. Mother
B. Father
C. Both equally
D. Environment

Correct Answer: B
Explanation: Father contributes either X or Y chromosome.

Section G: Mutation and Genetic Disorders

Q31. A sudden heritable change in DNA is called:

A. Variation
B. Recombination
C. Mutation
D. Transcription

Correct Answer: C
Explanation: Mutation alters genetic material.

Q32. Which is a gene mutation?

A. Down’s syndrome
B. Turner’s syndrome
C. Sickle cell anaemia
D. Klinefelter’s syndrome

Correct Answer: C
Explanation: Sickle cell anaemia is caused by a point mutation.

Q33. Trisomy 21 causes:

A. Turner’s syndrome
B. Down’s syndrome
C. Klinefelter’s syndrome
D. Haemophilia

Correct Answer: B
Explanation: Extra chromosome 21 leads to Down’s syndrome.

Q34. Turner’s syndrome genotype is:

A. XXY
B. XO
C. XXX
D. XYY

Correct Answer: B
Explanation: Females possess only one X chromosome.

Q35. Klinefelter’s syndrome occurs in:

A. Females only
B. Males only
C. Both sexes
D. Children only

Correct Answer: B
Explanation: XXY condition affects males.

Section H: Application & Competency-Based

Q36. Haemophilia follows which inheritance pattern?

A. Autosomal dominant
B. Autosomal recessive
C. X-linked recessive
D. Y-linked

Correct Answer: C
Explanation: Haemophilia is X-linked recessive.

Q37. Colour blindness is:

A. Autosomal disorder
B. X-linked recessive disorder
C. Dominant disorder
D. Chromosomal disorder

Correct Answer: B
Explanation: It is carried on X chromosome.

Q38. Nondisjunction occurs during:

A. DNA replication
B. Transcription
C. Meiosis
D. Translation

Correct Answer: C
Explanation: Failure of chromosome separation occurs in meiosis.

Q39. Which disorder is autosomal recessive?

A. Haemophilia
B. Colour blindness
C. Sickle cell anaemia
D. Turner’s syndrome

Correct Answer: C
Explanation: Two recessive alleles are required.

Q40. Genetic counselling is useful for:

A. Mutation prevention
B. Trait modification
C. Disease prediction
D. Cell division

Correct Answer: C
Explanation: It helps assess risk of inherited disorders.

Section I: Higher-Order Thinking MCQs

Q41. Which factor contradicts Mendel’s Law of Independent Assortment?

A. Mutation
B. Linkage
C. Codominance
D. Pleiotropy

Correct Answer: B
Explanation: Linked genes do not assort independently.

Q42. Genetic variation is increased mainly due to:

A. Dominance
B. Segregation
C. Recombination
D. Homozygosity

Correct Answer: C
Explanation: Recombination creates new gene combinations.

Q43. Which condition shows both genotype and phenotype ratio as 1:2:1?

A. Complete dominance
B. Codominance
C. Incomplete dominance
D. Linkage

Correct Answer: C
Explanation: Each genotype expresses a unique phenotype.

Q44. Multiple alleles arise due to:

A. Independent assortment
B. Segregation
C. Mutation over time
D. Fertilisation

Correct Answer: C
Explanation: Repeated mutations create allele variants.

Q45. Which statement is correct?

A. Genes always assort independently
B. Dominant alleles are more common
C. Alleles blend in offspring
D. Genes are located on chromosomes

Correct Answer: D
Explanation: Genes are physically located on chromosomes.

Section J: Board-Oriented MCQs

Q46. Which phase explains Law of Segregation?

A. Metaphase I
B. Anaphase I
C. Telophase I
D. Prophase II

Correct Answer: B
Explanation: Homologous chromosomes separate in anaphase I.

Q47. Which trait does NOT follow Mendelian inheritance?

A. Pea plant height
B. ABO blood group
C. Seed colour
D. Seed shape

Correct Answer: B
Explanation: ABO blood group shows codominance and multiple alleles.

Q48. Which disorder is caused by nondisjunction?

A. Sickle cell anaemia
B. Haemophilia
C. Down’s syndrome
D. Phenylketonuria

Correct Answer: C
Explanation: Nondisjunction leads to trisomy 21.

Q49. Gene mapping is based on:

A. Mutation rate
B. Recombination frequency
C. Dominance
D. Segregation

Correct Answer: B
Explanation: Recombination frequency reflects gene distance.

Q50. The basic unit of inheritance is:

A. Chromosome
B. DNA
C. Gene
D. Allele

Correct Answer: C
Explanation: Genes control specific traits and are inherited units.

✔ NCERT Strictly Aligned | ✔ CBSE Board Pattern | ✔ Concept-Clearing MCQs

🎯 Targeting Exams Section

This MCQ set is carefully designed to support preparation for the following examinations:

• CBSE Class 12 Biology Board Examination

• CBSE Compartment & Improvement Exams

• School Unit Tests and Pre-Board Examinations

• NEET (UG) – Concept Reinforcement Level

• Other Class 12 State Board Exams (NCERT-aligned)

The questions follow the latest CBSE competency-based MCQ pattern, focusing on conceptual clarity, application, and assertion-style reasoning.

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