7. There are two mutant plants. One shows taller phenotype than wild type, whereas the other has the same height as the wild type. When these two mutations were brought in together by genetic crosses, the double mutant displayed even taller phenotype than the tall mutant plants. This genetic interaction is called
(1) additive interaction.
(2) antagonistic interaction.
(3) synergistic interaction.
(4) suppressive interaction.

Explanation of the Genetic Interaction in Plant Height

When two mutant plants are crossed—one showing a taller phenotype than the wild type and the other showing wild-type height—and their double mutant offspring have an even taller phenotype, this describes a synergistic interaction. This interaction indicates the combined effect of two mutations exceeds the sum of their individual effects, enhancing the trait more than either mutation alone.​

Option Clarifications

• (1) Additive interaction: The effects of two genes simply add up, meaning the double mutant’s phenotype is the sum of individual mutations’ effects but not exceeding it.

• (2) Antagonistic interaction: One mutation’s effect counteracts or diminishes the effect of the other gene, leading to reduced or neutral phenotype in the double mutant.

• (3) Synergistic interaction: The combined effect of both mutations is greater than the sum of their separate effects, producing an enhanced phenotype such as increased height.

• (4) Suppressive interaction: One mutation masks or suppresses the effect of another, leading to a phenotype similar to one of the single mutants, not enhanced.

Genetic Interaction Types in Plants

In genetics, synergistic interactions often occur when genes participate in the same or complementary pathways affecting a trait like height. The observation that the double mutant has a taller phenotype than either single mutant confirms synergism where gene effects amplify each other rather than simply add or suppress.​

The correct answer for this question is (3) synergistic interaction because the double mutant’s phenotype surpassing that of the tall mutant demonstrates enhanced combined gene effects characteristic of synergy in genetic interactions.