Assertion (A): A true-breeding pea line shows stable trait inheritance and expression for several generations.
Reason (R): Mendel selected true-breeding pea plant varieties as pairs which were similar except for one character with contrasting traits.
In the light of the above statements, choose the correct answer from the options given below.
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Both (A) and (R) are correct, but (R) is not the correct explanation of (A).
Assertion (A): A true-breeding pea line shows stable trait inheritance and expression for several generations. — True. A is about what a true-breeding line is. Such a line shows the same trait, stably inherited and expressed, generation after generation.
Reason (R): Mendel selected true-breeding pea plant varieties as pairs which were similar except for one character with contrasting traits. — True. R is about how Mendel chose his plants. He selected 14 true-breeding varieties in pairs, each pair alike except for one character with contrasting traits.
Why R does not explain A? A line is stable because it has gone through continuous self-pollination for many generations. R does not speak of self-pollination at all. It tells us which true-breeding plants Mendel picked and how he paired them, which assumes the lines were already stable. The way plants were selected cannot be the reason for their stability, so R is true but is not the correct explanation of A.
NCERT Extract:
Mendel’s Laws of Inheritance – “… Mendel conducted such artificial pollination/cross pollination experiments using several true-breeding pea lines. A true-breeding line is one that, having undergone continuous self-pollination, shows the stable trait inheritance and expression for several generations. Mendel selected 14 true-breeding pea plant varieties, as pairs which were similar except for one character with contrasting traits.”