In a dihybrid cross involving RRTT(red tall) ×rrtt(white dwarf), what will be the ratio of red & tall plants in `F_(2)` generation -

Options

A. `3:1`
B. `1:1`
C. `1:2`
D. `2:3`

Answer

To solve the question regarding the dihybrid cross of RRTT (red tall) and rrtt (white dwarf) and to find the ratio of red and tall plants in the F2 generation, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Parental Genotypes**:
- The parental plants are RRTT (red tall) and rrtt (white dwarf).
- Here, R (red) is dominant over r (white), and T (tall) is dominant over t (dwarf).

2. **Determine the F1 Generation**:
- When RRTT is crossed with rrtt, all offspring in the F1 generation will be heterozygous for both traits: RrTt.
- Therefore, the genotype of the F1 generation is RrTt, which will express the dominant traits (red and tall).

3. **Self-Fertilization of F1 Generation**:
- The F1 plants (RrTt) will be self-fertilized to produce the F2 generation.
- The gametes produced by RrTt will be RT, Rt, rT, and rt.

4. **Construct a Punnett Square**:
- Set up a 4x4 Punnett square using the gametes from the F1 generation:
```
RT Rt rT rt
-------------------------
RT | RRTT | RRTt | RrTT | RrTt |
-----------------------------------
Rt | RRTt | RRtt | RrTt | Rrtt |
-----------------------------------
rT | RrTT | RrTt | rrTT | rrTt |
-----------------------------------
rt | RrTt | Rrtt | rrTt | rrtt |
```
- From this Punnett square, we can count the phenotypes.

5. **Count the Phenotypes**:
- The phenotypes can be categorized as follows:
- Red Tall (R_T): RRTT, RRTt, RrTT, RrTt (9 total)
- Red Dwarf (R_tt): RRtt, Rrtt (3 total)
- White Tall (rrT_): rrTT, rrTt (3 total)
- White Dwarf (rrtt): rrtt (1 total)

6. **Calculate the Ratios**:
- The phenotypic ratio in the F2 generation is 9 (red tall) : 3 (red dwarf) : 3 (white tall) : 1 (white dwarf).
- To find the ratio of red and tall plants, we can combine the counts of red tall and white tall plants.
- Total red plants = 9 (red tall) + 3 (red dwarf) = 12
- Total tall plants = 9 (red tall) + 3 (white tall) = 12
- Therefore, the ratio of red to tall plants is 12:12, which simplifies to 1:1.

### Final Answer:
The ratio of red and tall plants in the F2 generation is **1:1**.