In a dihybrid cross, when one pair of alleles show incomplete dominance, genotypic ratio comes to

Options

A. `3:6:3:1:2:1`
B. `1:2:2:4:12:1:2:1`
C. `9:3:3:1`
D. `1:2:1`

Answer

To solve the problem of finding the genotypic ratio in a dihybrid cross where one pair of alleles shows incomplete dominance, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Incomplete Dominance**:
- Incomplete dominance occurs when neither allele is completely dominant over the other, leading to a blending of traits in the heterozygous condition. For example, if we have alleles A (red) and a (white), the heterozygous condition (Aa) may result in a pink phenotype.

2. **Set Up the Dihybrid Cross**:
- A dihybrid cross involves two traits, each represented by a pair of alleles. Let's denote the first trait as A/a (incomplete dominance) and the second trait as B/b (complete dominance).
- For the dihybrid cross, we can use parents with genotypes AaBb (heterozygous for both traits) crossed with AaBb.

3. **Determine Gametes**:
- Each parent can produce four types of gametes due to the combination of alleles: AB, Ab, aB, and ab.
- Thus, the gametes from both parents will be combined in a 4x4 Punnett square.

4. **Construct the Punnett Square**:
- Create a 4x4 Punnett square to visualize the combinations of the gametes:
```
AB Ab aB ab
-------------------------
AB | AABB AABb AaBB AaBb
Ab | AABb AAbb AaBb Aabb
aB | AaBB AaBb aaBB aaBb
ab | AaBb Aabb aaBb aabb
```

5. **Count the Genotypes**:
- Now, we will count the occurrences of each genotype:
- AABB: 1
- AABb: 2
- AAbb: 1
- AaBB: 2
- AaBb: 4
- Aabb: 2
- aaBB: 1
- aaBb: 2
- aabb: 1

6. **Calculate the Genotypic Ratio**:
- The genotypic ratio can be summarized as follows:
- 1 AABB : 2 AABb : 1 AAbb : 2 AaBB : 4 AaBb : 2 Aabb : 1 aaBB : 2 aaBb : 1 aabb
- This results in a total of 16 genotypes.

7. **Final Genotypic Ratio**:
- The final genotypic ratio can be expressed as:
- 1 : 2 : 1 : 2 : 4 : 2 : 1 : 2 : 1