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 question regarding the genotypic ratio in a dihybrid cross when one pair of alleles shows incomplete dominance, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Dihybrid Cross**:
- A dihybrid cross involves two traits, each represented by a pair of alleles. For example, consider traits A (with alleles A and a) and B (with alleles B and b).

2. **Identify Incomplete Dominance**:
- Incomplete dominance occurs when the phenotype of the heterozygote is intermediate between the phenotypes of the homozygotes. For example, if A (red) and a (white) show incomplete dominance, the heterozygote (Aa) might be pink.

3. **Set Up the Punnett Square**:
- For a dihybrid cross involving one trait with incomplete dominance, we can set up a Punnett square. For example, if we have A/a for one trait and B/b for the other, we can cross AaBb x AaBb.

4. **Determine Gametes**:
- The gametes produced from AaBb would be AB, Ab, aB, and ab. Since one trait shows incomplete dominance, we will consider the combinations of alleles for that trait.

5. **Fill in the Punnett Square**:
- The Punnett square will have 16 boxes (4x4) since we are crossing two dihybrids. Each box will represent a combination of alleles from the parents.

6. **Count Genotypes**:
- After filling in the Punnett square, we can count the genotypes. For example, if we find:
- 1 AABB (homozygous dominant for both traits)
- 2 AABb (homozygous dominant for first trait, heterozygous for second)
- 2 AaBB (heterozygous for first trait, homozygous dominant for second)
- 4 AaBb (heterozygous for both traits)
- 2 Aabb (heterozygous for first trait, homozygous recessive for second)
- 1 aabb (homozygous recessive for both traits)

7. **Genotypic Ratio**:
- The genotypic ratio in this case will be 1:2:1 for the incomplete dominance trait combined with the typical dihybrid ratio. Thus, the overall genotypic ratio will be 1:2:1:2:4:2:1.

### Final Answer:
The genotypic ratio in a dihybrid cross when one pair of alleles shows incomplete dominance is **1:2:1:2:4:2:1**.