Test cross is when

Options

A. `F_1`crossed with heterozygous parent
B. `F_1` crossed with heterozygous dominant parent
C. `F_1` crossed with homozygous recessive parent
D. `F_1` crossed with homozygous parent

Answer

### Step-by-Step Solution:

1. **Understanding Test Cross**:
- A test cross is a genetic cross used to determine the genotype of an individual exhibiting a dominant phenotype. It helps in identifying whether the individual is homozygous dominant or heterozygous.

2. **Identifying the Cross**:
- In a test cross, the individual in question (F1 generation) is crossed with a homozygous recessive individual. This is crucial because the homozygous recessive individual will only contribute recessive alleles.

3. **Analyzing the Results**:
- After performing the test cross, the offspring's phenotypic ratio is analyzed:
- If the ratio of dominant to recessive phenotypes in the offspring is 1:1, it indicates that the F1 individual is heterozygous (having one dominant and one recessive allele).
- If the ratio deviates from 1:1, it suggests that the F1 individual is homozygous dominant (having two dominant alleles).

4. **Conclusion**:
- Therefore, the correct answer to the question "Test cross is when" is: **F1 is crossed with a homozygous recessive parent**.

### Final Answer:
- **Test cross is when F1 is crossed with a homozygous recessive parent.**