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 a case of multiple allelism
D. the alleles of two genes are segregat- ing independently

Answer

To solve the question regarding the significance of the `9:3:3:1` ratio in a dihybrid cross, we can break down the explanation into clear steps.

### Step-by-Step Solution:

1. **Understanding Dihybrid Cross**:
A dihybrid cross involves two traits, each represented by two alleles. For example, consider traits A (dominant A, recessive a) and B (dominant B, recessive b).

2. **Setting Up the Punnett Square**:
When performing a dihybrid cross, we can use a Punnett square to visualize the genetic combinations. Each parent can produce four types of gametes (AB, Ab, aB, ab) due to the independent assortment of alleles.

3. **Calculating the Phenotypic Ratio**:
When we cross two heterozygous individuals (AaBb x AaBb), the resulting offspring can be categorized into four phenotypic groups:
- 9 offspring with the dominant phenotype for both traits (A_B_)
- 3 offspring with the dominant phenotype for the first trait and recessive for the second (A_bb)
- 3 offspring with the recessive phenotype for the first trait and dominant for the second (aaB_)
- 1 offspring with the recessive phenotype for both traits (aabb)

4. **Interpreting the Ratio**:
The resulting phenotypic ratio of `9:3:3:1` indicates that:
- The majority (9) exhibit both dominant traits.
- A smaller number (3) exhibit one dominant and one recessive trait.
- Another smaller number (3) exhibit the reverse (one recessive and one dominant).
- The least (1) exhibit both recessive traits.

5. **Conclusion**:
The `9:3:3:1` ratio denotes that the alleles of the two genes assort independently during gamete formation, as described by Mendel's law of independent assortment. This means that the inheritance of one trait does not affect the inheritance of another trait.

### Final Answer:
In a dihybrid cross, a `9:3:3:1` ratio denotes that the alleles of two genes assort independently during gamete formation.

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