Which of the following phenotypic ratio was found by Mendel in `F_(2)` generation of a dihybrid cross ?

Options

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

Answer

To determine the phenotypic ratio found by Mendel in the F2 generation of a dihybrid cross, we can follow these steps:

### Step 1: Understand Dihybrid Cross
A dihybrid cross involves two traits, each represented by two alleles. For example, let's consider traits A (dominant) and a (recessive) for the first trait, and B (dominant) and b (recessive) for the second trait.

### Step 2: Parental Generation (P Generation)
In the P generation, we start with two homozygous parents:
- One parent is homozygous dominant for both traits (AABB).
- The other parent is homozygous recessive for both traits (aabb).

### Step 3: First Filial Generation (F1 Generation)
When we cross these two parents (AABB x aabb), all offspring in the F1 generation will be heterozygous for both traits (AaBb).

### Step 4: Second Filial Generation (F2 Generation)
When we self-fertilize the F1 generation (AaBb x AaBb), we can use a Punnett square to determine the genotypes of the F2 generation. This results in a variety of combinations of alleles.

### Step 5: Determine the Phenotypic Ratio
From the Punnett square, we find the following phenotypic combinations:
- A_B_ (both dominant traits): 9
- A_bb (dominant for A, recessive for B): 3
- aaB_ (recessive for A, dominant for B): 3
- aabb (both recessive traits): 1

This gives us a total phenotypic ratio of:
**9:3:3:1**

### Step 6: Conclusion
The correct answer to the question regarding the phenotypic ratio found by Mendel in the F2 generation of a dihybrid cross is **9:3:3:1**.