Tt `xx` tt is

Options

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

Answer

To solve the question regarding the genetic cross Tt `xx` tt, we need to identify the type of cross being described. Let's break it down step by step.

### Step-by-Step Solution:

1. **Identify the Genotypes**: The given genotypes are Tt (heterozygous tall) and tt (homozygous dwarf). The capital "T" represents the dominant trait (tall), while "t" represents the recessive trait (dwarf).

2. **Understand the Cross**: The cross is between Tt and tt. This means we are crossing a heterozygous tall plant with a homozygous dwarf plant.

3. **Determine the Type of Cross**:
- A **test cross** is defined as a cross between an individual with an unknown genotype (in this case, Tt) and a homozygous recessive individual (tt).
- The purpose of a test cross is to determine the genotype of the unknown parent by observing the phenotypes of the offspring.

4. **Analyze the Options**:
- **Test Cross**: This is correct because we are crossing Tt with tt.
- **Back Cross**: This involves crossing F1 generation with one of its parents, which is not the case here.
- **Hybridization**: This refers to the interbreeding of genetically distinct individuals, which does not apply to this specific cross.
- **Reciprocal Cross**: This involves switching the roles of the male and female in the cross, which is also not applicable here.

5. **Conclusion**: Since the cross is between a heterozygous tall plant (Tt) and a homozygous recessive dwarf plant (tt), it is classified as a **test cross**.

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

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