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

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 dominant (TT) or heterozygous (Tt), we can perform a specific type of genetic cross known as a **test cross**. Here’s a step-by-step breakdown of how to approach this problem:

### Step 1: Understand the Genotypes
- The tall pea plant can either be homozygous dominant (TT) or heterozygous (Tt).
- The homozygous recessive genotype for the height trait is represented by "tt," which results in dwarf plants.

### Step 2: Perform a Test Cross
- A test cross involves crossing the tall pea plant (unknown genotype: TT or Tt) with a homozygous recessive plant (tt).
- This allows us to analyze the offspring's phenotypes to infer the genotype of the tall plant.

### Step 3: Analyze the Offspring
- If the tall plant is **homozygous dominant (TT)**:
- All offspring will be tall (100% tall plants).
- If the tall plant is **heterozygous (Tt)**:
- The offspring will show a 1:1 phenotypic ratio, resulting in 50% tall plants and 50% dwarf plants.

### Step 4: Conclusion
- By observing the phenotypes of the offspring from the test cross, we can determine the genotype of the tall pea plant:
- If all offspring are tall, the genotype is TT.
- If there are both tall and dwarf offspring, the genotype is Tt.

### Final Answer
The cross that should be performed to determine whether the genotype of the tall pea plant is TT or Tt is a **test cross**.

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