Which of the following crosses and resultant phenotypic ratios are mismatched?

Options

A. Tt x Tt - 3:1
B. tt x Tt - 2:1
C. TtYy x ttyy - 1:1:1:1
D. TtYy x TtYy - 9:3:3:1

Answer

To solve the question regarding mismatched crosses and resultant phenotypic ratios, we will analyze each option step by step.

### Step 1: Analyze the First Cross
- **Cross**: Heterozygous tall (Tt) × Heterozygous tall (Tt)
- **Gametes Produced**: Both parents produce two types of gametes: T and t.
- **Punnett Square Outcome**:
- TT (tall)
- Tt (tall)
- Tt (tall)
- tt (dwarf)
- **Phenotypic Ratio**: 3 tall : 1 dwarf
- **Conclusion**: This option is correctly matched.

### Step 2: Analyze the Second Cross
- **Cross**: Dwarf plant (tt) × Tall plant (Tt)
- **Gametes Produced**:
- Dwarf (tt) produces only t.
- Tall (Tt) produces T and t.
- **Punnett Square Outcome**:
- Tt (tall)
- tt (dwarf)
- **Phenotypic Ratio**: 1 tall : 1 dwarf
- **Conclusion**: The ratio given (2:1) is incorrect. This option is mismatched.

### Step 3: Analyze the Third Cross
- **Cross**: TtYy × Ttyy
- **Gametes Produced**:
- TtYy produces four types: TY, Ty, tY, ty.
- Ttyy produces two types: Ty, ty.
- **Punnett Square Outcome**:
- Combining the gametes gives four combinations.
- **Phenotypic Ratio**: 1:1:1:1
- **Conclusion**: This option is correctly matched.

### Step 4: Analyze the Fourth Cross
- **Cross**: Dihybrid cross (TtYy × TtYy)
- **Gametes Produced**: Each parent produces four types of gametes: TY, Ty, tY, ty.
- **Punnett Square Outcome**:
- 9:3:3:1 ratio for the phenotypes.
- **Conclusion**: This option is correctly matched.

### Final Conclusion
The mismatched pair is the second option: Dwarf plant (tt) crossed with Tall plant (Tt) resulting in a phenotypic ratio of 2:1, which should actually be 1:1.

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