In a dihybrid crossm if you get `9:3:3:1` ratio it denotes that

Options

A. the alleles of two genes are interacting with each other
B. it is a multigenic inheritance
C. it is case of multiple allelism
D. the alleles of two genes are segregating independently

Explanation

### Step-by-Step Text Solution:

1. **Understanding Dihybrid Cross**: A dihybrid cross involves two traits, each represented by two alleles. For example, consider the traits of seed shape (Round - R, Wrinkled - r) and seed color (Yellow - Y, Green - y).

2. **Mendel's Law of Independent Assortment**: According to Mendel's law of independent assortment, alleles for different traits segregate independently during gamete formation. This means that the inheritance of one trait does not affect the inheritance of another trait.

3. **Gamete Formation**: In a dihybrid cross between two heterozygous parents (RrYy x RrYy), the possible gametes produced are RY, Ry, rY, and ry. Each gamete carries one allele from each gene.

4. **Punnett Square**: Constructing a Punnett square for the dihybrid cross will help visualize the combinations of alleles. The Punnett square will have 16 boxes, representing all possible combinations of the gametes.

5. **Phenotypic Ratio**: When you fill in the Punnett square, you will find the following phenotypic ratio:
- 9 Round Yellow (R_Y_)
- 3 Round Green (R_yy)
- 3 Wrinkled Yellow (rrY_)
- 1 Wrinkled Green (rryy)

6. **Conclusion**: The resulting phenotypic ratio of 9:3:3:1 indicates that the two traits are assorting independently, confirming that the alleles of two genes are segregating independently.

### Final Answer:
The `9:3:3:1` ratio in a dihybrid cross denotes that the alleles of two genes are segregating independently.

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