📘 Inheritance of one gene|| Class 12 Biology
Directions (Standard CBSE Pattern):
A. Both Assertion and Reason are true and Reason is the correct explanation
B. Both Assertion and Reason are true but Reason is not the correct explanation
C. Assertion is true but Reason is false
D. Assertion is false but Reason is true
Question 1
Assertion (A): All F₁ plants of a monohybrid cross are tall.
Reason (R): Tallness is a dominant trait over dwarfness.
✅ Correct Answer: A
Explanation: Tall allele (T) masks dwarf allele (t) in heterozygous condition, resulting in all tall plants in F₁ generation.
Question 2
Assertion (A): Recessive traits reappear in the F₂ generation.
Reason (R): Alleles segregate during gamete formation.
✅ Correct Answer: A
Explanation: Law of segregation explains separation of alleles, allowing recessive traits to express again in F₂ generation.
Question 3
Assertion (A): Phenotypic ratio of a monohybrid cross is 3 : 1.
Reason (R): Three genotypes are formed in the F₂ generation.
✅ Correct Answer: B
Explanation: Both are true, but the phenotypic ratio occurs due to dominance, not merely because of three genotypes.
Question 4
Assertion (A): Homozygous recessive individuals express recessive traits.
Reason (R): Recessive alleles express only in the absence of dominant alleles.
✅ Correct Answer: A
Explanation: Recessive traits appear only when dominant alleles are absent.
Question 5
Assertion (A): Test cross helps in identifying the genotype of a dominant individual.
Reason (R): Test cross involves crossing with a homozygous recessive individual.
✅ Correct Answer: A
Explanation: The appearance of offspring reveals whether the dominant individual is homozygous or heterozygous.
Question 6
Assertion (A): F₁ generation individuals are heterozygous in monohybrid cross.
Reason (R): Each individual receives one allele from each parent.
✅ Correct Answer: A
Explanation: Gametes carry one allele each, producing heterozygous offspring in F₁ generation.
Question 7
Assertion (A): Genotypic ratio of monohybrid cross is 1 : 2 : 1.
Reason (R): Gametes are produced in unequal proportions.
✅ Correct Answer: C
Explanation: Gametes are produced in equal proportions; unequal gametes is incorrect.
Question 8
Assertion (A): Law of dominance explains uniformity of F₁ generation.
Reason (R): Dominant allele suppresses the expression of recessive allele.
✅ Correct Answer: A
Explanation: Dominance causes only one trait to express in F₁ generation.
Question 9
Assertion (A): Law of segregation is universally applicable.
Reason (R): Alleles separate during meiosis.
✅ Correct Answer: A
Explanation: Segregation of alleles is a fundamental event during meiosis in all organisms.
Question 10
Assertion (A): Genes controlling a character are present in pairs.
Reason (R): One allele is inherited from each parent.
✅ Correct Answer: A
Explanation: Diploid organisms inherit one allele from each parent.
Question 11
Assertion (A): Dwarf plants appear only in F₂ generation of Mendel’s experiment.
Reason (R): Dwarfness is a recessive trait.
✅ Correct Answer: A
Explanation: Recessive traits remain hidden in F₁ and reappear in F₂.
Question 12
Assertion (A): Phenotype of an organism depends only on genotype.
Reason (R): Environment has no role in trait expression.
✅ Correct Answer: D
Explanation: Phenotype depends on both genotype and environment.
Question 13
Assertion (A): Monohybrid inheritance follows Mendelian laws.
Reason (R): Only one gene is involved in controlling the trait.
✅ Correct Answer: B
Explanation: Both are true, but Mendelian laws apply regardless of number of genes studied.
Question 14
Assertion (A): Homozygous individuals produce only one type of gamete.
Reason (R): Both alleles are identical.
✅ Correct Answer: A
Explanation: Identical alleles lead to identical gametes.
Question 15
Assertion (A): Mendel is called the father of genetics.
Reason (R): He discovered laws of inheritance using pea plants.
✅ Correct Answer: A
Explanation: Mendel laid the foundation of classical genetics.