Question

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R.
Assertion A: In an experiment, Mendel observed that the \(F_1\) progeny plants are all tall and none are dwarf.
Reason R: Stem height is a contrasting trait, with tall being dominant and dwarf being recessive.
In the light of the above statements, choose the most appropriate answer from the options given below:

• A. A is not correct but R is correct
• B. Both A and R are correct and R is the correct explanation of A
• C. Both A and R are correct but R is not the correct explanation of A
• D. A is correct but R is not correct

Hint:

The monohybrid phenotypic ratio in \(F_2\) is \(3:1\) (Tall : Dwarf), while the genotypic ratio is \(1:2:1\) (\(TT : Tt : tt\)). The recessive trait only expresses itself under homozygous conditions (\(tt\)), which is why it disappears in the \(F_1\) generation and reappears in \(F_2\).

Answer 1

The Correct Option is B

Step 1: Set up Mendel's cross.
Mendel crossed true-breeding tall pea plants ($TT$) with true-breeding dwarf plants ($tt$) and observed the first generation, the $F_1$.
Step 2: Work out the $F_1$ genotype.
Each $F_1$ plant gets $T$ from one parent and $t$ from the other, so all $F_1$ plants are $Tt$, that is heterozygous.
Step 3: Check Assertion A.
Assertion A says all $F_1$ plants are tall and none are dwarf. Since all are $Tt$ and tall is expressed, this observation is correct.
Step 4: Check Reason R.
Reason R states tall is dominant and dwarf is recessive. This is a true statement about the contrasting trait of stem height.
Step 5: Link the two by the Law of Dominance.
In a heterozygote, the dominant allele masks the recessive one. So tall being dominant is exactly why the $Tt$ plants look tall and the dwarf trait stays hidden.
Step 6: Conclude the relationship.
R correctly explains A, so both are true and R is the correct explanation, matching option 2.
\[ \boxed{\text{Both A and R are correct and R is the correct explanation of A}} \]