Case Study–1: Mendel’s Height Experiment
Gregor Mendel crossed a pure tall pea plant (TT) with a pure dwarf pea plant (tt).
All plants in the F₁ generation were tall. When F₁ plants were self-pollinated,
both tall and dwarf plants appeared in the F₂ generation.
1. What was the genotype of F₁ generation plants?
A. TT
B. tt
C. Tt
D. TTT
✅ Answer: C. Tt
F₁ plants received one allele from each parent, making them heterozygous (Tt).
2. Why were all F₁ plants tall?
A. Because dwarf allele disappeared
B. Because tall allele is dominant
C. Due to mutation
D. Due to environment
✅ Answer: B
Tall allele (T) is dominant and masks the recessive dwarf allele (t).
3. Which Mendelian law explains the F₁ result?
A. Law of segregation
B. Law of independent assortment
C. Law of dominance
D. Law of linkage
✅ Answer: C
Law of dominance explains uniformity of F₁ generation.
4. What is the phenotypic ratio in F₂ generation?
A. 1 : 1
B. 1 : 2 : 1
C. 3 : 1
D. 9 : 3 : 3 : 1
✅ Answer: C
Three tall and one dwarf plant appear in the F₂ generation.
Case Study–2: Reappearance of Recessive Trait
5. Why does the recessive trait disappear in F₁ generation?
A. It is destroyed
B. It mutates
C. It is masked by dominant allele
D. It is not inherited
✅ Answer: C
Dominant allele suppresses the expression of recessive allele.
6. Which law explains the reappearance of the recessive trait?
A. Law of dominance
B. Law of segregation
C. Law of independent assortment
D. Chromosomal theory
✅ Answer: B
Alleles separate during gamete formation, allowing recessive allele to express.
7. During which process do alleles segregate?
A. Mitosis
B. Fertilization
C. Meiosis
D. Transcription
✅ Answer: C
Segregation of alleles occurs during meiosis.
Case Study–3: Test Cross Experiment
8. What was the genotype of the tall parent?
A. TT
B. tt
C. Tt
D. TTT
✅ Answer: C
Appearance of dwarf offspring indicates heterozygous genotype.
9. What type of cross is this?
A. Monohybrid cross
B. Dihybrid cross
C. Test cross
D. Back cross
✅ Answer: C
Crossing with a homozygous recessive individual is a test cross.
10. Why is homozygous recessive parent used in test cross?
A. It is dominant
B. It shows variation
C. It reveals genotype clearly
D. It mutates easily
✅ Answer: C
Recessive parent helps identify the unknown genotype.
Case Study–4: Gamete Formation
11. How many types of gametes are produced?
A. One
B. Two
C. Three
D. Four
✅ Answer: B
Heterozygous individual produces two types of gametes (T and t).
12. Which law is supported by this observation?
A. Law of dominance
B. Law of segregation
C. Law of linkage
D. Law of variation
✅ Answer: B
Separation of alleles supports the law of segregation.
Case Study–5: Genotype vs Phenotype
13. Why are genotypic and phenotypic ratios different?
A. Due to mutation
B. Due to dominance
C. Due to environment
D. Due to unequal gametes
✅ Answer: B
Heterozygous and homozygous dominant individuals look the same phenotypically.
14. Which genotype(s) show dominant phenotype?
A. TT only
B. Tt only
C. TT and Tt
D. tt only
✅ Answer: C
Both TT and Tt express the dominant trait.
15. Which genotype expresses recessive phenotype?
A. TT
B. Tt
C. tt
D. TTT
✅ Answer: C
Recessive phenotype appears only in homozygous recessive condition.