Question

The dwarf variety of garden pea plants are now known to have a mutation in a gene needed for synthesis of gibberellin. $F_1$ plant obtained by Mendel from the tall (TT) $\times$ dwarf (tt) cross were tall.
Which of the following inferences can be drawn from the given information?
(i) Gibberellin causes elongation of stems.
(ii) Heterozygous (Tt) plants produce the same amount of gibberellin as homozygous dominant (TT) plants.
(iii) Gibberellin induces production of auxin.
(iv) Mutation may have occurred in a gene producing an enzyme.

• A. (i) and (ii)
• B. (ii), (iii) and (iv)
• C. (i), (ii), (iii) and (iv)
• D. (i), (ii) and (iv)

Answer 1

The correct option is D (i), (ii) and (iv)

The data given says that dwarf plants have mutated genes for gibberellin synthesis, it indicates that gibberellin causes elongation of stems. As both heterozygous (Tt) and homozygous dominant (TT) plants obtained from the cross between tall (TT) and dwarf (tt) plants are tall, it indicates that both of them produce the same amount of gibberellin. A mutation that has affected gibberellin synthesis may be one that resulted in non-synthesis of a protein that functions as an enzyme during the process of gibberellin synthesis. The data says nothing about the relationship between gibberellin and auxin, thus the inference (iii) cannot be made.