The genotype of a plant showing the dominant phenotype can be determined by:

Options

A. test cross
B. dihybird cross
C. pedigree analysis
D. back cross.

Explanation

To determine the genotype of a plant showing a dominant phenotype, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Dominant Phenotype**:
- A dominant phenotype can be expressed by either a homozygous dominant genotype (AA) or a heterozygous genotype (Aa).

2. **Identify the Recessive Parent**:
- To determine the genotype of the plant with the dominant phenotype, we need to use a plant that is homozygous recessive (aa) for the trait in question.

3. **Perform a Test Cross**:
- A test cross involves crossing the plant with the dominant phenotype (which could be either AA or Aa) with the homozygous recessive plant (aa).

4. **Analyze the Offspring**:
- After the test cross, observe the phenotypes of the offspring:
- If all offspring display the dominant phenotype, the genotype of the parent with the dominant phenotype is likely homozygous dominant (AA).
- If the offspring show a 1:1 ratio of dominant to recessive phenotypes, the genotype of the dominant phenotype parent is heterozygous (Aa).

5. **Conclusion**:
- Based on the results of the test cross, we can confidently determine whether the plant with the dominant phenotype is homozygous (AA) or heterozygous (Aa).