Which of these crosses will be performed to determine whether the genotype of the tall pea plant is TT or Tr ?

Options

A. Reciprocal cross
B. Dihybrid cross
C. Test cross
D. Back cross

Answer

To determine whether the genotype of a tall pea plant is homozygous (TT) or heterozygous (Tt), we can perform a specific type of genetic cross. Here’s a step-by-step solution:

### Step-by-Step Solution:

1. **Understanding the Traits**:
- The tallness trait (T) is dominant, and the dwarfness trait (t) is recessive.
- A tall plant can either be homozygous (TT) or heterozygous (Tt).

2. **Identifying the Cross Needed**:
- To determine the genotype of the tall plant, we need to see how it behaves when crossed with a known genotype.
- The best way to do this is to cross the tall plant with a recessive individual (tt).

3. **Performing the Test Cross**:
- This specific cross, where the tall plant (unknown genotype) is crossed with a homozygous recessive plant (tt), is called a **test cross**.
- The offspring from this cross will help us determine the genotype of the tall plant.

4. **Analyzing the Offspring**:
- If the tall plant is homozygous (TT), all offspring will be tall (100% tall).
- If the tall plant is heterozygous (Tt), the offspring will be in a 1:1 ratio of tall to dwarf (50% tall and 50% dwarf).

5. **Conclusion**:
- By observing the phenotypes of the offspring, we can conclude whether the tall plant is homozygous (TT) or heterozygous (Tt).

### Final Answer:
The correct answer is **C. Test Cross**.