In a dihybrid cross between two heterozygotes, AaBb `xx` AaBb, if we get a 3:1 ratio among offspring, the reason would be

Options

A. Polygenes
B. Linked genes
C. Pleiotropic gene
D. Hypostatic gene

Answer

To solve the question regarding the dihybrid cross between two heterozygotes (AaBb x AaBb) resulting in a 3:1 ratio among offspring, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Dihybrid Cross**:
- A dihybrid cross involves two traits, each represented by two alleles. In this case, we have two genes (A and B), each with two alleles (A, a and B, b).

2. **Expected Ratio in Dihybrid Cross**:
- When two heterozygotes (AaBb) are crossed, the expected phenotypic ratio for two independently assorting traits is typically 9:3:3:1. This means we would expect 9 offspring with both dominant traits, 3 with the dominant trait of the first gene and recessive of the second, 3 with the recessive trait of the first gene and dominant of the second, and 1 with both recessive traits.

3. **Identifying the Given Ratio**:
- The question states that a 3:1 ratio is observed among the offspring. This suggests that one of the traits is not assorting independently with the other.

4. **Understanding the Reason for 3:1 Ratio**:
- A 3:1 ratio typically arises in a monohybrid cross (Aa x Aa) where one trait is dominant over the other. However, in this case, the presence of a 3:1 ratio in a dihybrid cross indicates that the two genes are linked.

5. **Linkage of Genes**:
- Linked genes are genes that are located close to each other on the same chromosome and tend to be inherited together. Because of this linkage, the expected independent assortment does not occur, leading to a skewed ratio among the offspring.

6. **Conclusion**:
- Therefore, the reason for obtaining a 3:1 ratio in the offspring of the dihybrid cross AaBb x AaBb is due to the presence of linked genes.

### Final Answer:
The correct answer is **linked genes**.

---