In a typical Mendelian cross, which is a dihybrid cross, one parent is homozygous for both dominant traits and another parent is homozygous for both recessive traits. In the `F_(2)` -generation, both parental combination and recombinantions appear. The phenotypic ratio of parental combinations to recombinations is

Options

A. 2.42
B. 1.50
C. 1.37
D. 1.66

Answer

To solve the problem regarding the phenotypic ratio of parental combinations to recombinations in a typical Mendelian dihybrid cross, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Cross**:
- We have two traits, let's say Trait A and Trait B.
- One parent is homozygous dominant for both traits (AA BB).
- The other parent is homozygous recessive for both traits (aa bb).

2. **F1 Generation**:
- When these two parents are crossed, all offspring (F1 generation) will be heterozygous for both traits (Aa Bb).
- The F1 generation will display the dominant phenotype for both traits.

3. **Selfing the F1 Generation**:
- When we self the F1 generation (Aa Bb x Aa Bb), we need to determine the phenotypic ratios in the F2 generation.

4. **Using the Punnett Square**:
- A dihybrid cross can be represented using a 4x4 Punnett square.
- The possible gametes from Aa Bb are AB, Ab, aB, and ab.
- The resulting combinations in the F2 generation will yield the following phenotypic ratio:
- 9 (A_B_) : 3 (A_bb) : 3 (aaB_) : 1 (aabb)

5. **Identifying Parental and Recombinant Types**:
- Parental combinations (same as the parents) are:
- A_B_ (dominant for both traits)
- aabb (recessive for both traits)
- Recombinant combinations (different from the parents) are:
- A_bb (dominant for A, recessive for B)
- aaB_ (recessive for A, dominant for B)

6. **Counting the Combinations**:
- From the phenotypic ratio:
- Parental combinations = 9 (A_B_) + 1 (aabb) = 10
- Recombinant combinations = 3 (A_bb) + 3 (aaB_) = 6

7. **Calculating the Ratio**:
- The ratio of parental combinations to recombinant combinations is:
- Parental:Recombinant = 10:6
- This simplifies to 5:3.

### Final Answer:
The phenotypic ratio of parental combinations to recombinations in the F2 generation is **5:3**.