Assertion–Reason Questions

📘 Mendel's law || Class 12 Biology

Directions (CBSE Pattern):

For each question, choose the correct option:

A. Both Assertion and Reason are true and Reason is the correct explanation of Assertion
B. Both Assertion and Reason are true but Reason is NOT the correct explanation of Assertion
C. Assertion is true but Reason is false
D. Assertion is false but Reason is true

Question 1

Assertion (A): In a monohybrid cross, the F₁ generation shows only one type of phenotype.

Reason (R): The dominant allele masks the expression of the recessive allele.

✅ Correct Option: A

Explanation: In F₁ generation, all offspring are heterozygous and express only the dominant trait due to the Law of Dominance.

Question 2

Assertion (A): Recessive traits reappear in the F₂ generation.

Reason (R): Alleles segregate during gamete formation.

✅ Correct Option: A

Explanation: The Law of Segregation explains the separation of alleles during meiosis, allowing recessive traits to reappear.

Question 3

Assertion (A): The phenotypic ratio of a monohybrid cross in F₂ generation is 3:1.

Reason (R): Gametes carry only one allele of a gene.

✅ Correct Option: A

Explanation: Each gamete carries one allele due to segregation, producing the 3:1 phenotypic ratio.

Question 4

Assertion (A): The Law of Independent Assortment applies only to unlinked genes.

Reason (R): Linked genes are present on the same chromosome.

✅ Correct Option: A

Explanation: Genes on the same chromosome tend to be inherited together and do not assort independently.

Question 5

Assertion (A): A dihybrid cross produces a phenotypic ratio of 9:3:3:1 in F₂ generation.

Reason (R): Alleles of different genes assort independently.

✅ Correct Option: A

Explanation: Independent assortment of two gene pairs results in the 9:3:3:1 ratio.

Question 6

Assertion (A): The genotype Tt is called heterozygous.

Reason (R): It contains two identical alleles.

✅ Correct Option: C

Explanation: Tt contains two different alleles, not identical.

Question 7

Assertion (A): Homozygous recessive individuals express recessive traits.

Reason (R): Recessive alleles express themselves only in absence of dominant alleles.

✅ Correct Option: A

Question 8

Assertion (A): Mendel selected pea plants because they show clear contrasting traits.

Reason (R): Pea plants reproduce only by cross-pollination.

✅ Correct Option: C

Question 9

Assertion (A): Law of segregation is also known as the law of purity of gametes.

Reason (R): Each gamete receives only one allele of a gene.

✅ Correct Option: A

Question 10

Assertion (A): Independent assortment occurs during meiosis.

Reason (R): Homologous chromosomes separate randomly during meiosis.

✅ Correct Option: A

Question 11

Assertion (A): The genotype TT always produces tall plants.

Reason (R): TT contains two dominant alleles.

✅ Correct Option: A

📘 Explanation: Presence of dominant alleles ensures expression of dominant trait.

Question 12

Assertion (A): A test cross is useful to determine the genotype of an organism.

Reason (R): The organism is crossed with a homozygous recessive individual.

✅ Correct Option: A

📘 Explanation: The phenotypes of offspring reveal the unknown genotype.

Question 13.

Assertion (A): Linked genes do not follow Mendel’s law of independent assortment.

Reason (R): They are inherited together due to their proximity on the chromosome.

✅ Correct Option: A

📘 Explanation: Physical closeness on chromosome prevents independent assortment.

Question 14.

Assertion (A): Mendel used statistical analysis in his experiments.

Reason (R): He studied inheritance by observing only one generation.

✅ Correct Option: C

📘 Explanation: Mendel studied multiple generations, not just one.

Question 15.

Assertion (A): Phenotype depends on genotype.

Reason (R): Genotype determines the expression of traits.

✅ Correct Option: A

📘 Explanation: Genetic constitution controls physical appearance.

Question 16.

Assertion (A): The F₂ generation shows more variation than F₁ generation.

Reason (R): F₂ generation contains different combinations of alleles.

✅ Correct Option: A

📘 Explanation: Recombination in F₂ increases variation.

Question 17.

Assertion (A): The basic unit of inheritance is a gene.

Reason (R): Genes are segments of DNA located on chromosomes.

✅ Correct Option: A

📘 Explanation: Genes carry hereditary information.

Question 18.

Assertion (A): Codominance is an exception to Mendel’s law of dominance.

Reason (R): Both alleles express themselves equally in heterozygous condition.

✅ Correct Option: A

📘 Explanation: Neither allele masks the other in codominance.

Question 19.

Assertion (A): Mendel’s laws form the basis of modern genetics.

Reason (R): They explain inheritance of traits from parents to offspring.

✅ Correct Option: A

📘 Explanation: Modern genetics builds upon Mendel’s principles.

Question 20.

Assertion (A): Independent assortment increases genetic variation.

Reason (R): It produces new combinations of traits.

✅ Correct Option: A

📘 Explanation: Random assortment leads to diversity in offspring.