Assertion–Reason Questions

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 humans, the sex of a child is determined by the father.

Reason (R): Male produces two types of gametes, X-bearing and Y-bearing sperms.

✅ Correct Option: A

Explanation: Female produces only X-bearing ova, while male produces X and Y sperms; hence father determines sex.

Question 2

Assertion (A): Human females are homogametic.

Reason (R): They produce only one type of gamete with respect to sex chromosome.

✅ Correct Option: A

Explanation: Females have XX chromosomes and produce only X-bearing ova.

Question 3

Assertion (A): Human males are heterogametic.

Reason (R): They produce two types of sperms containing X and Y chromosomes.

✅ Correct Option: A

Explanation: Presence of X and Y chromosomes makes males heterogametic.

Question 4

Assertion (A): The Y chromosome is essential for male sex determination in humans.

Reason (R): It carries the SRY gene responsible for initiating male development.

✅ Correct Option: A

Explanation: SRY gene on Y chromosome triggers testis formation.

Question 5

Assertion (A): Absence of Y chromosome always results in female development.

Reason (R): The default pathway of human development is female.

✅ Correct Option: A

Explanation: Without SRY gene, female development occurs.

Question 6

Assertion (A): In birds, females are heterogametic.

Reason (R): Birds follow ZZ–ZW type of sex determination.

✅ Correct Option: A

Explanation: ZW females produce Z and W gametes.

Question 7

Assertion (A): In honey bees, males are diploid.

Reason (R): They develop from fertilized eggs.

❌ Correct Option: D

Explanation: Males are haploid and develop from unfertilized eggs.

Question 8

Assertion (A): Haplodiploid sex determination is controlled by chromosome number.

Reason (R): Males are haploid while females are diploid.

✅ Correct Option: A

Explanation: Chromosome number determines sex in honey bees.

Question 9

Assertion (A): Environmental sex determination does not involve genes.

Reason (R): Temperature influences sex in some reptiles.

✅ Correct Option: B

Explanation: Genes are present, but environment influences sex outcome.

Question 10

Assertion (A): Sex determination and sex differentiation are the same processes.

Reason (R): Both occur at fertilization.

❌ Correct Option: D

Explanation: Sex determination occurs at fertilization; differentiation occurs later.

Question 11

Assertion (A): XX–XO system lacks Y chromosome.

Reason (R): Males possess only one X chromosome.

✅ Correct Option: A

Explanation: XO males do not have Y chromosome.

Question 12

Assertion (A): In ZZ–ZW system, males are homogametic.

Reason (R): They possess identical sex chromosomes.

✅ Correct Option: A

Explanation: ZZ males produce only Z gametes.

Question 13

Assertion (A): Sex ratio in humans is approximately 1:1.

Reason (R): Equal numbers of X and Y sperms are produced.

✅ Correct Option: A

Explanation: Random fertilization results in equal sex ratio.

Question 14

Assertion (A): The X chromosome carries many genes unrelated to sex.

Reason (R): It is larger than the Y chromosome.

✅ Correct Option: A

Explanation: X chromosome is gene-rich.

Question 15

Assertion (A): Sex determination in humans is environmentally controlled.

Reason (R): Temperature decides sex in reptiles.

❌ Correct Option: D

Explanation: Human sex determination is genetic, not environmental.

Question 16

Assertion (A): In haplodiploid organisms, males do not have fathers.

Reason (R): They develop from unfertilized eggs.

✅ Correct Option: A

Explanation: Unfertilized eggs develop into males.

Question 17

Assertion (A): Sex differentiation depends on hormones.

Reason (R): Hormones influence development of reproductive organs.

✅ Correct Option: A

Explanation: Hormonal action leads to differentiation after determination.

Question 18

Assertion (A): Sex chromosomes are also called autosomes.

Reason (R): They determine body traits.

❌ Correct Option: D

Explanation: Sex chromosomes are called allosomes, not autosomes.

Question 19

Assertion (A): The Y chromosome is genetically inactive.

Reason (R): It carries the SRY gene.

❌ Correct Option: C

Explanation: Y chromosome is not inactive; SRY gene is functional.

Question 20

Assertion (A): Sex determination is fixed at the zygote stage in humans.

Reason (R): Sex chromosomes are established during fertilization.

✅ Correct Option: A

Explanation: Chromosomal combination is decided at fertilization.

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.