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.
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).
Question 462 of 519
📘 CLASS XII
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.
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.
Question 463 of 519
📘 CLASS XII
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.
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).
Question 464 of 519
📘 CLASS XII
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.
A true-breeding line exhibits stability (A). This stability is achieved because the line has undergone continuous self-pollination (R), resulting in homozygosity.
Question 465 of 519
📘 CLASS XII
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.
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.
Question 466 of 519
📘 CLASS XII
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.
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.
Question 467 of 519
📘 CLASS XII
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.
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.
Question 468 of 519
📘 CLASS XII
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.
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.
Question 469 of 519
📘 CLASS XII
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.
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.
Question 470 of 519
📘 CLASS XII
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.
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).
