1 : 1 : 1 : 1 ratio of progenies can be obtained if the plants employed for crossing are
(A.) `"TTRR"xx"ttRR"`
(B.) `"TtRR"xx"ttrr"`
(C.) `"TtRR"xx"ttrr"`
(D.) `"TtRR" xx"ttRR"`

Options

A. A , C and D
B. A, B , C and D
C. B and D
D. A and B

Answer

To solve the problem of determining which crossing of plants will yield a 1:1:1:1 ratio of progenies, we need to analyze the given options in terms of their genetic makeup. The ratio of 1:1:1:1 typically arises from a test cross involving a dihybrid cross.

### Step-by-Step Solution:

1. **Understanding the Genetic Notation**:
- The letters represent different traits. For example, "T" represents tall plants (dominant), and "t" represents dwarf plants (recessive). Similarly, "R" represents round seeds (dominant), and "r" represents wrinkled seeds (recessive).
- The combinations of these letters indicate whether the plant is homozygous (both alleles the same) or heterozygous (one dominant and one recessive allele).

2. **Identifying the Crosses**:
- We need to evaluate each option to see if it involves a test cross with a homozygous recessive plant (ttrr) which will yield a 1:1:1:1 ratio.

3. **Analyzing Each Option**:
- **Option A: "TTRR" x "ttRR"**
- This cross involves two dominant traits (TT and RR) and one recessive trait (tt). This will not yield a 1:1:1:1 ratio.

- **Option B: "TtRR" x "ttrr"**
- Here, "TtRR" is heterozygous for height and homozygous dominant for seed shape, while "ttrr" is homozygous recessive for both traits. This can yield a 1:1:1:1 ratio:
- Possible offspring: TtRR (Tall, Round), Ttrr (Tall, Wrinkled), ttRR (Dwarf, Round), ttrr (Dwarf, Wrinkled).

- **Option C: "TtRR" x "ttrr"**
- This is identical to Option B and will yield the same 1:1:1:1 ratio for the same reasons.

- **Option D: "TtRR" x "ttRR"**
- In this case, "TtRR" is heterozygous for height and homozygous for seed shape, while "ttRR" is homozygous recessive for height and homozygous dominant for seed shape. This will not yield a 1:1:1:1 ratio.

4. **Conclusion**:
- The only options that yield a 1:1:1:1 ratio of progenies are **Option B ("TtRR" x "ttrr")** and **Option C ("TtRR" x "ttrr")**.

### Final Answer:
The correct options are **(B) "TtRR" x "ttrr"** and **(C) "TtRR" x "ttrr"**.