🧬 Case-Based Questions

Mendelian Genetics Practice

Case Study 1: Monohybrid Cross (Plant Height)
Mendel crossed a pure tall pea plant (TT) with a pure dwarf pea plant (tt). All plants in the F₁ generation were tall. When these F₁ plants were allowed to self-pollinate, tall and dwarf plants appeared in the F₂ generation in a definite ratio.
1. Why were all F₁ plants tall?
A. Dwarf allele was absent
B. Tall allele is dominant
C. F₁ plants were homozygous
D. Dwarf allele was destroyed
✅ Answer: B
Tall allele (T) is dominant and masks the recessive dwarf allele (t).
2. Which law explains the uniformity of F₁ generation?
A. Law of segregation
B. Law of independent assortment
C. Law of dominance
D. Law of linkage
✅ Answer: C
3. What is the genotypic ratio of F₂ generation?
A. 3 : 1
B. 1 : 2 : 1
C. 9 : 3 : 3 : 1
D. 1 : 1
✅ Answer: B
4. Why did dwarf plants reappear in F₂ generation?
A. Mutation occurred
B. Tall allele was lost
C. Alleles segregated during gamete formation
D. Environmental factors
✅ Answer: C
Case Study 2: Dihybrid Cross (Seed Shape & Colour)
Mendel crossed round yellow seeds (RRYY) with wrinkled green seeds (rryy). All F₁ plants were round yellow. F₂ generation showed four phenotypes.
5. Which traits are dominant?
A. Wrinkled and green
B. Round and green
C. Round and yellow
D. Wrinkled and yellow
✅ Answer: C
6. Which law is verified?
A. Dominance
B. Segregation
C. Independent assortment
D. Purity of gametes
✅ Answer: C
7. Phenotypic ratio in F₂?
A. 3 : 1
B. 1 : 2 : 1
C. 9 : 3 : 3 : 1
D. 12 : 3 : 1
✅ Answer: C
8. Gamete types from RrYy?
A. 2
B. 3
C. 4
D. 8
✅ Answer: C
Case Study 3: Law of Segregation
9. Genotype of parents?
A. TT × TT
B. tt × tt
C. Tt × Tt
D. TT × tt
✅ Answer: C
10. Which law explains dwarf plants?
A. Dominance
B. Independent assortment
C. Segregation
D. Chromosomal theory
✅ Answer: C
Case Study 4: Test Cross
11. Genotype of tall plant?
A. TT
B. Tt
C. tt
D. TTT
✅ Answer: B
12. Type of cross?
A. Monohybrid
B. Dihybrid
C. Test cross
D. Back cross
✅ Answer: C
Case Study 5: Genetic Variation
13. Why more variation in F₂?
A. Mutation
B. Dominant traits disappear
C. New combinations of alleles
D. Environment changes genes
✅ Answer: C
14. Main process responsible?
A. Mitosis
B. Meiosis
C. Transcription
D. Translation
✅ Answer: B
Case Study 6: Chromosomal Theory of Inheritance
15. Which meiotic event explains segregation?
A. Crossing over
B. Pairing of chromosomes
C. Separation of homologous chromosomes
D. DNA replication
✅ Answer: C