To determine which cross would yield a phenotypic ratio of 1:1:1:1, we need to analyze the given crosses step by step.
### Step 1: Understand the Crosses
We are given four options for genetic crosses. We need to analyze each option to see how many different types of offspring (phenotypes) they produce and in what ratio.
### Step 2: Analyze Each Cross
1. **Option A: TtRr x ttrr**
- Parent 1 (TtRr) can produce gametes: TR, Tr, tR, tr (4 types).
- Parent 2 (ttrr) can only produce gametes: tr (1 type).
- Possible combinations: TtRr, Ttrr, ttRr, ttrr.
- Resulting phenotypes: Tall Round (TtRr), Tall Wrinkled (Ttrr), Dwarf Round (ttRr), Dwarf Wrinkled (ttrr).
- Ratio: 1:1:1:1 (4 phenotypes).
2. **Option B: TT RR x tt rr**
- Parent 1 (TT RR) can produce only one type of gamete: TR (1 type).
- Parent 2 (tt rr) can only produce one type of gamete: tr (1 type).
- Resulting phenotype: All offspring will be Tall Round (TTRR).
- Ratio: 1 (all same phenotype).
3. **Option C: TtRr x Ttrr**
- Parent 1 (TtRr) can produce gametes: TR, Tr, tR, tr (4 types).
- Parent 2 (Ttrr) can produce gametes: Tr, tr (2 types).
- Possible combinations: TTRr, Ttrr, ttRr, ttrr.
- Resulting phenotypes: Tall Round (TTRr), Tall Wrinkled (Ttrr), Dwarf Round (ttRr), Dwarf Wrinkled (ttrr).
- Ratio: 1:1:1:1 (4 phenotypes).
4. **Option D: TtRr x TtRr**
- Parent 1 (TtRr) can produce gametes: TR, Tr, tR, tr (4 types).
- Parent 2 (TtRr) can produce gametes: TR, Tr, tR, tr (4 types).
- Resulting phenotypes: Tall Round, Tall Wrinkled, Dwarf Round, Dwarf Wrinkled.
- Ratio: 9:3:3:1 (not 1:1:1:1).
### Step 3: Conclusion
From the analysis, we find that **Option A** and **Option C** both yield a ratio of 1:1:1:1. However, since the question asks for a specific cross, we can conclude that the correct answer is **Option C**.
### Final Answer
The cross that would yield a ratio of 1:1:1:1 is **Option C: TtRr x Ttrr**.
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