Incomplete dominance in plants is a type of inheritance where neither allele is completely dominant over the other. As a result, the heterozygous offspring show an intermediate trait — a blend between the two parental traits.
This means the offspring’s appearance is a mixture of both parents, rather than showing only one parent’s trait.
Example:
In the four o’clock plant (Mirabilis jalapa), when a plant with red flowers (RR) is crossed with a plant having white flowers (rr), the resulting F₁ generation has pink flowers (Rr).
This happens because the red allele is not fully dominant over the white one.
So, in incomplete dominance:
- RR → red flowers
- rr → white flowers
- Rr → pink flowers
In short: Incomplete dominance occurs when the heterozygote shows a blended or intermediate phenotype between the two parents.