Test cross is performed to know the genotype. It is cross between

Options

A. (a) `F_(1)` hybrid with dominant parent
B. (b) `F_(2)` hybrid with dominant parent
C. (c) two `F_(1)` hybrids
D. (d) None of the above

Explanation

**Step-by-Step Solution:**

1. **Understanding Test Cross:**
- A test cross is a genetic cross used to determine the genotype of an organism that exhibits a dominant phenotype. The organism's genotype could either be homozygous dominant (TT) or heterozygous (Tt).

2. **Identifying the Cross:**
- In a test cross, the organism with the unknown genotype (dominant phenotype) is crossed with a homozygous recessive organism (tt). This is crucial because the recessive parent will only contribute recessive alleles.

3. **Possible Outcomes of the Cross:**
- If the dominant phenotype parent is homozygous (TT):
- All offspring will display the dominant phenotype (tall in this case).
- If the dominant phenotype parent is heterozygous (Tt):
- The offspring will show a 1:1 ratio of dominant to recessive phenotypes (50% tall and 50% short).

4. **Conclusion Based on Offspring:**
- By analyzing the offspring's phenotypes, one can infer the genotype of the dominant phenotype parent:
- If all offspring are tall, the parent is homozygous dominant (TT).
- If there is a mix of tall and short offspring, the parent is heterozygous (Tt).

5. **Evaluating the Options:**
- Option A: F1 hybrid with dominant parent - Incorrect, as we cross with a recessive parent.
- Option B: F2 hybrid with dominant parent - Incorrect, as we cross with a recessive parent.
- Option C: 2 F1 hybrids - Incorrect, as we need to cross with a recessive parent.
- Option D: None of the above - Correct, as the test cross is specifically between a dominant phenotype parent and a recessive homozygous parent.

**Final Answer:**
The test cross is performed between a dominant phenotype parent (whose genotype is unknown) and a recessive homozygous parent (tt). Therefore, the correct answer is D: None of the above.

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