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 problem of determining the ratio of red and tall plants in the F2 generation from a dihybrid cross of RRTT (red tall) and rrt (white dwarf), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Parental Genotypes**:
- The parental plants are RRTT (red tall) and rrt (white dwarf).
- Here, R (dominant) represents red color and r (recessive) represents white color.
- T (dominant) represents tallness and t (recessive) represents dwarf.

2. **Determine the F1 Generation**:
- When we cross RRTT with rrt, all offspring in the F1 generation will have the genotype RrTt.
- This means all F1 plants will be red and tall because they possess at least one dominant allele for each trait.

3. **Self-Fertilization of F1 Generation**:
- The F1 plants (RrTt) will be self-fertilized to produce the F2 generation.
- The genotype of F1 plants can be represented as RrTt.

4. **Use a Punnett Square for Dihybrid Cross**:
- To find the phenotypic ratio in the F2 generation, we can use a Punnett square.
- The gametes from RrTt will be RT, Rt, rT, and rt.
- The resulting F2 generation will have the following phenotypic ratio:
- 9 red tall (R_T_)
- 3 red dwarf (R_tt)
- 3 white tall (rrT_)
- 1 white dwarf (rrtt)
- This gives us a total phenotypic ratio of 9:3:3:1.

5. **Calculate the Ratio of Red and Tall Plants**:
- To find the ratio of red plants, we add the red tall (9) and red dwarf (3) plants: 9 + 3 = 12.
- To find the ratio of tall plants, we add the tall red (9) and tall white (3) plants: 9 + 3 = 12.
- Therefore, the ratio of red plants to tall plants in the F2 generation is 12:12.

6. **Simplify the Ratio**:
- The ratio 12:12 can be simplified to 1:1.

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