Which one of the mentioned characters does not represent the true breeding line?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A true breeding line is one that shows the X-linked recessive trait.
Option (1) A true breeding line is one that shows the stable trait inheritance. — Represents a true breeding line. In such a line the trait passes unchanged from parents to offspring. A tall true-breeding pea plant gives only tall plants.
Option (2) A true breeding line is one that shows the X-linked recessive trait. — Does not represent a true breeding line. “X-linked” tells where a gene lies: on the X chromosome. It says nothing about whether a line breeds true. The pea plants Mendel used have no X chromosome at all.
Option (3) A true breeding line is one that having undergone continuous self-pollination. — Represents a true breeding line. Self-pollination over many generations makes the plants homozygous, so they pass on the same alleles every time.
Option (4) A true breeding line is one that shows stable expression for several generations. — Represents a true breeding line. The trait shows up in the same way in every generation. Mendel chose such lines so that any new form in his crosses came from the cross itself.
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.”