A monohybid cross between two plants, one having 22cm long internodes and the other having 12 cm long internodes, produced `F_(1)` hybrids all off 18 cm long internodes. This is a case of

Options

A. incomplete dominance
B. complete dominance
C. multiple allelism
D. recessive dominants

Explanation

To solve the question regarding the monohybrid cross between two plants with different internode lengths, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Parent Plants**:
- One plant has internodes measuring 22 cm (let's denote this as the tall plant).
- The other plant has internodes measuring 12 cm (let's denote this as the dwarf plant).

2. **Understand the Cross**:
- When these two plants are crossed, we are looking at a monohybrid cross, which typically involves one trait (in this case, internode length).

3. **Analyze the F1 Generation**:
- The F1 hybrids produced from this cross all have internodes measuring 18 cm. This is an intermediate length between the two parent plants.

4. **Determine the Type of Inheritance**:
- In a typical dominant-recessive relationship, we would expect the F1 generation to resemble one of the parents (either tall or dwarf). However, since the F1 hybrids are intermediate (18 cm), this suggests that neither allele is completely dominant over the other.

5. **Conclude the Type of Inheritance**:
- The situation described is an example of **incomplete dominance**. Incomplete dominance occurs when the phenotype of the heterozygote (F1) is intermediate between the phenotypes of the two homozygotes (the parent plants).

6. **Final Answer**:
- Therefore, the answer to the question is that this is a case of **incomplete dominance**.