Tallness (T-) is dominant over dwarfness (tt) while red flower colour (R-) is dominant over white colour (rr). A plant with genotype TtRr is crossed with plant of genotype ttrr. Percentage of progeny having tall plants with red flower is

Options

A. 0.25
B. 0.5
C. 0.75
D. 1

Answer

To solve the problem, we need to determine the percentage of progeny that are tall plants with red flowers when a plant with genotype TtRr is crossed with a plant of genotype ttrr.

### Step-by-Step Solution:

1. **Identify the Genotypes and Traits**:
- Tallness (T) is dominant over dwarfness (t).
- Red flower color (R) is dominant over white flower color (r).
- The first plant has genotype TtRr (tall with red flowers).
- The second plant has genotype ttrr (dwarf with white flowers).

2. **Determine the Gametes**:
- The first plant (TtRr) can produce four types of gametes:
- TR (Tall, Red)
- Tr (Tall, White)
- tR (Dwarf, Red)
- tr (Dwarf, White)
- The second plant (ttrr) can only produce one type of gamete:
- tr (Dwarf, White)

3. **Set Up the Punnett Square**:
- We will create a Punnett square to visualize the combinations of gametes from both parents.
- The gametes from TtRr are placed on one side, and the gametes from ttrr are placed on the other side.

| | tr |
|-------|--------|
| TR | TtRr |
| Tr | Ttrr |
| tR | ttRr |
| tr | ttrr |

4. **Determine the Genotypes of the Progeny**:
- From the Punnett square, we can identify the genotypes of the offspring:
- TtRr (Tall, Red)
- Ttrr (Tall, White)
- ttRr (Dwarf, Red)
- ttrr (Dwarf, White)

5. **Identify the Phenotypes**:
- Now we categorize the phenotypes:
- TtRr: Tall with Red flowers
- Ttrr: Tall with White flowers
- ttRr: Dwarf with Red flowers
- ttrr: Dwarf with White flowers

6. **Calculate the Percentage of Tall Plants with Red Flowers**:
- Out of the four possible combinations, only one (TtRr) represents tall plants with red flowers.
- Therefore, the percentage of progeny that are tall plants with red flowers is:
\[ \text{Percentage} = \left( \frac{\text{Number of TtRr}}{\text{Total Number of Progeny}} \right) \times 100 = \left( \frac{1}{4} \right) \times 100 = 25\% \]

### Final Answer:
The percentage of progeny having tall plants with red flowers is **25%**.

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