Assertion (A):
James Dewey Watson received his B.Sc. degree in Zoology in 1947.
Reason (R):
He received his Ph.D. degree in 1950 on a study of the effect of hard X-rays on bacteriophage multiplication.

[Principles-of-Inheritance-and-Variation] [class-xii ]

• (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
Correct Option: B  [ B ]

Remark: Both statements (A and R) are true biographical facts about Watson's academic career. However, the Ph.D. topic (R) does not explain why he received his B.Sc. in Zoology (A).

Assertion (A):
Gregor Mendel conducted hybridisation experiments on garden peas for seven years (1856-1863).
Reason (R):
Based on these experiments, he proposed the fundamental Laws of Inheritance in living organisms.

[Principles-of-Inheritance-and-Variation] [class-xii ]

• (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
Correct Option: B  [ B ]

Remark: Both A and R are true historical facts concerning Mendel's work. The fact that he proposed the laws (R) resulted from the experiments (A), but R does not explain why the experiments took seven years.

Assertion (A):
Mendel applied statistical analysis and mathematical logic to problems in biology for the first time.
Reason (R):
His experiments had a large sampling size, which gave greater credibility to the data he collected.

[Principles-of-Inheritance-and-Variation] [class-xii ]

• (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
Correct Option: B  [ B ]

Remark: Both statements are correct facts about Mendel's methodology. However, the large sampling size (R) is a factor that utilized A (mathematical analysis) effectively, but it does not explain *why* he adopted the unique approach of using mathematics in biology (A).

Assertion (A):
A true-breeding pea line shows stable trait inheritance and expression for several generations.
Reason (R):
A true-breeding line has undergone continuous self-pollination.

[Principles-of-Inheritance-and-Variation] [class-xii ]

• (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
Correct Option: A  [ A ]

Remark: A true-breeding line exhibits stability (A). This stability is achieved because the line has undergone continuous self-pollination (R), resulting in homozygosity.

Assertion (A):
In a monohybrid cross between tall (TT) and dwarf (tt) plants, none of the F₁ progeny were of in-between height.
Reason (R):
The Law of Segregation is based on the fact that the alleles do not show any blending.

[Principles-of-Inheritance-and-Variation] [class-xii ]

• (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
Correct Option: A  [ A ]

Remark: The observation that there was no blending (A) is directly explained by the core principle of the Law of Segregation (R), which states that alleles do not blend.

Assertion (A):
In a pair of dissimilar factors (alleles), the dominant factor (T) masks the recessive factor (t).
Reason (R):
This phenomenon is called the Law of Dominance and explains why only one parental character is expressed in the F₁ generation.

[Principles-of-Inheritance-and-Variation] [class-xii ]

• (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
Correct Option: A  [ A ]

Remark: The Law of Dominance (R) states that one factor dominates the other in a dissimilar pair (A) and uses this relationship to explain the expression seen in the F₁ generation.

Assertion (A):
The F₂ genotypic ratio of 1/4 TT : 1/2 Tt : 1/4 tt is mathematically condensable.
Reason (R):
This ratio is the expansion of the binomial expression (1/2T + 1/2t)^2, based on the equal frequency (1/2) of T and t gametes.

[Principles-of-Inheritance-and-Variation] [class-xii ]

• (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
Correct Option: A  [ A ]

Remark: The F₂ ratio can be condensed into the binomial expression (A). R provides the exact mathematical derivation showing that this expression equals the observed ratio.

Assertion (A):
When examining a dominant trait in an F₂ plant, it is impossible to know its genotypic composition (TT or Tt) by visual inspection alone.
Reason (R):
A Test Cross is performed by crossing the organism showing the dominant phenotype with the recessive parent.

[Principles-of-Inheritance-and-Variation] [class-xii ]

• (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
Correct Option: B  [ B ]

Remark: A is True: The phenotype of TT and Tt are identical (Tall), creating ambiguity. R is True: R defines the Test Cross method. However, R is the *solution* (the procedure performed) to the problem described in A, but R does not explain *why* the ambiguity (A) exists.

Assertion (A):
In the snapdragon flower, incomplete dominance results in an F₂ phenotypic ratio of 1:2:1 (Red: Pink: White).
Reason (R):
The underlying F₂ genotypic ratio remains 1:2:1, and the lack of complete dominance makes it possible to distinguish the heterozygous pink phenotype.

[Principles-of-Inheritance-and-Variation] [class-xii ]

• (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
Correct Option: A  [ A ]

Remark: In incomplete dominance (A), the phenotypic ratio matches the genotypic ratio 1:2:1 (R). R explains this by noting that incomplete dominance allows the intermediate heterozygote (Pink) to be distinguished.

Assertion (A):
In co-dominance, the F₁ generation resembles both parents.
Reason (R):
When the $I^A$ and $I^B$ alleles are present together, they both express their own types of sugars simultaneously, resulting in the AB blood type.

[Principles-of-Inheritance-and-Variation] [class-xii ]

• (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
Correct Option: A  [ A ]

Remark: Co-dominance results in the expression of both parental traits (A). The ABO blood group example illustrates this, where $I^A$ and $I^B$ both express their specific sugars simultaneously (R).