A test cross is performed

Options

A. by selfing of `F_(2)`-generation plants
B. by selfing of `f_(1)`-generation plants
C. to determine whether `F_(1)`-plant is homozgous or heterozygous
D. between a homozygous dominant and homozygous recessive plant

Answer

### Step-by-Step Solution:

1. **Understanding the Test Cross**:
A test cross is a genetic cross performed to determine the genotype of an individual exhibiting a dominant phenotype. The individual in question could either be homozygous dominant (TT) or heterozygous (Tt).

2. **Identifying the Genotypes**:
- Homozygous dominant: TT (tall)
- Heterozygous: Tt (tall)
- Homozygous recessive: tt (dwarf)

3. **Performing the Test Cross**:
To perform a test cross, you cross the individual with a homozygous recessive individual (tt). This will help in determining whether the dominant phenotype is homozygous or heterozygous.

4. **Crossing the Genotypes**:
- If the test cross is between TT (homozygous dominant) and tt (homozygous recessive):
- Gametes from TT: T, T
- Gametes from tt: t, t
- Offspring: All offspring will be Tt (tall).

- If the test cross is between Tt (heterozygous) and tt (homozygous recessive):
- Gametes from Tt: T, t
- Gametes from tt: t, t
- Offspring: 50% Tt (tall) and 50% tt (dwarf).

5. **Analyzing the Results**:
- If all offspring are tall, the original plant was homozygous dominant (TT).
- If there is a 1:1 ratio of tall to dwarf plants, then the original plant was heterozygous (Tt).

6. **Conclusion**:
The test cross is a reliable method to determine the genotype of an individual with a dominant phenotype by analyzing the phenotypes of the offspring produced.