Observe the four crosses given below :
(A.) `"TTrr"xx"ttRR"`
(B.) `"TtRr"xx"ttrr"`
(C.) `"TtRr"xx"TTrr"`
(D.) `"Ttrr"xx"ttRr"`
In which of the following crosses , 1: 1: 1: 1 ratio of progenies is obtained ?

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, we need to analyze each of the given crosses to determine which ones yield a 1:1:1:1 ratio of progeny. This ratio indicates that all four possible combinations of traits are produced in equal proportions. We will examine each cross step by step.

### Step 1: Analyze Cross A - "TTrr" x "ttRR"
1. **Parent Genotypes**:
- Parent 1: TTrr (homozygous tall, homozygous wrinkled)
- Parent 2: ttRR (homozygous dwarf, homozygous round)
2. **Gametes Produced**:
- Parent 1 can only produce: TR
- Parent 2 can only produce: tr
3. **Offspring**:
- All offspring will be TtRr (tall and round).
4. **Ratio**: Only one phenotype (tall and round) is produced.
5. **Conclusion**: This cross does not yield a 1:1:1:1 ratio.

### Step 2: Analyze Cross B - "TtRr" x "ttrr"
1. **Parent Genotypes**:
- Parent 1: TtRr (heterozygous tall, heterozygous round)
- Parent 2: ttrr (homozygous dwarf, homozygous wrinkled)
2. **Gametes Produced**:
- Parent 1 can produce: TR, Tr, tR, tr
- Parent 2 can produce: tr
3. **Offspring**:
- Cross combinations:
- TtRr (tall, round)
- Ttrr (tall, wrinkled)
- ttRr (dwarf, round)
- ttrr (dwarf, wrinkled)
4. **Ratio**: All four phenotypes are produced in equal proportions.
5. **Conclusion**: This cross yields a 1:1:1:1 ratio.

### Step 3: Analyze Cross C - "TtRr" x "TTrr"
1. **Parent Genotypes**:
- Parent 1: TtRr (heterozygous tall, heterozygous round)
- Parent 2: TTrr (homozygous tall, homozygous wrinkled)
2. **Gametes Produced**:
- Parent 1 can produce: TR, Tr, tR, tr
- Parent 2 can produce: Tr
3. **Offspring**:
- Cross combinations:
- TTRr (tall, round)
- TtRr (tall, round)
- Ttrr (tall, wrinkled)
4. **Ratio**: Only three phenotypes are produced (tall and round, tall and wrinkled).
5. **Conclusion**: This cross does not yield a 1:1:1:1 ratio.

### Step 4: Analyze Cross D - "Ttrr" x "ttRr"
1. **Parent Genotypes**:
- Parent 1: Ttrr (heterozygous tall, homozygous wrinkled)
- Parent 2: ttrr (homozygous dwarf, homozygous round)
2. **Gametes Produced**:
- Parent 1 can produce: Tr, tr
- Parent 2 can produce: tr
3. **Offspring**:
- Cross combinations:
- TtRr (tall, round)
- Ttrr (tall, wrinkled)
- ttRr (dwarf, round)
- ttrr (dwarf, wrinkled)
4. **Ratio**: All four phenotypes are produced in equal proportions.
5. **Conclusion**: This cross yields a 1:1:1:1 ratio.

### Final Conclusion:
The crosses that yield a 1:1:1:1 ratio of progeny are:
- Cross B: "TtRr" x "ttrr"
- Cross D: "Ttrr" x "ttRr"

### Answer:
**Crosses B and D yield a 1:1:1:1 ratio of progeny.**