Principles of Inheritance and Variation – important questions for Boards 2027

CBSE Class 12 Biology

1. MCQ · 1 mark

   For how long did Mendel conduct hybridisation experiments on garden peas before proposing laws of inheritance? A. 1856–1863 B. 1846–1853 C. 1865–1872 D. 1875–1882

   Answer

   (A) 1856–1863 — Mendel conducted hybridisation experiments on garden peas for seven years.

2. SA · 1.5 marks

   State two features of Mendel’s experimental approach that supported his conclusions about inheritance.

   Answer

   1. Mendel applied statistical analysis and mathematical logic to biological problems and used a large sampling size, giving greater credibility to his data. 2. He confirmed his inferences through experiments on successive generations, showing that his results pointed to general rules of inheritance.

3. SA · 2 marks

   State the law of segregation and explain what each gamete receives during gamete formation.

   Answer

   The law of segregation states that the alleles of a pair separate during gamete formation. Each gamete receives only one allele; alleles do not blend, and both characters can be recovered in the F₂ generation.

4. MA · 3 marks

   Describe the haplodiploid sex-determination system in honey bees. Include how fertilised and unfertilised eggs develop and the chromosome numbers and ploidy of females and males.

   Answer

   1. In honey bees, sex determination is based on the number of sets of chromosomes an individual receives. 2. An offspring formed from the union of a sperm and an egg develops as a female (queen or worker), whereas an unfertilised egg develops as a male (drone) by parthenogenesis. 3. Females are diploid, with 32 chromosomes, and males are haploid, with 16 chromosomes.

5. LA · 4 marks

   What is pedigree analysis? Explain how representing a trait in a family tree over generations provides an alternative to controlled crosses for studying inheritance in humans.

   Answer

   Pedigree analysis traces the inheritance of a particular trait through a family tree over generations. 1. Controlled crosses, which can be performed in pea plants or some other organisms, are not possible in human beings. Therefore, direct experimental crosses cannot be used to study human inheritance. 2. The family history of a particular trait provides an alternative. Records of the trait among family members allow its inheritance to be followed across generations. 3. In pedigree analysis, the inheritance pattern of the trait is represented in a family tree over several generations. The representation makes it possible to examine how the trait passes between family members. 4. Pedigree study can trace a specific trait, abnormality or disease in human genetics. It can also help reveal whether an inherited trait is associated with an altered gene or chromosome. Thus, pedigree analysis is a useful method for studying inheritance in humans.

6. LA · 5 marks

   Define a true-breeding line. Describe how Mendel selected pea varieties for his crosses, and give examples of contrasting traits he studied.

   🔒 Answer locked. Unlock all answers on SmartKalike

7. VLA · 6 marks

   Explain why the law of segregation shows that alleles do not blend. Describe the kinds and proportions of gametes produced by homozygous and heterozygous parents.

   🔒 Answer locked. Unlock all answers on SmartKalike

8. MCQ · 1 mark

   In a dihybrid cross involving seed shape and seed colour, which is the expected F₂ phenotypic ratio for round yellow, wrinkled yellow, round green and wrinkled green plants? (A) 9:3:3:1 (B) 3:1:3:1 (C) 1:2:1:2 (D) 9:3:1:3

   🔒 Answer locked. Unlock all answers on SmartKalike

9. SA · 1.5 marks

   State the law of dominance, explaining what happens when a pair of factors is dissimilar. How do factors occur in relation to a character?

   🔒 Answer locked. Unlock all answers on SmartKalike

10. SA · 2 marks

    How can a functioning allele and a modified, non-functional allele account for the phenotype of an individual?

    🔒 Answer locked. Unlock all answers on SmartKalike