What is the ratio of homozygous plants for both dominant characters in F, of a dihybrid cross?

Options

A. `1/16`
B. `3/16`
C. `4/16`
D. `9/16`

Answer

To determine the ratio of homozygous plants for both dominant characters in the F1 generation of a dihybrid cross, we can follow these steps:

### Step 1: Understand the Dihybrid Cross
A dihybrid cross involves two traits, each represented by two alleles. For example, let's consider:
- Trait 1: Tall (T) vs. Dwarf (t)
- Trait 2: Yellow (Y) vs. Green (y)

### Step 2: Determine the Genotypes of the Parents
Assuming we start with two homozygous parents:
- Parent 1: TTYY (tall and yellow)
- Parent 2: ttyy (dwarf and green)

### Step 3: Perform the Cross
When we cross these two parents, all offspring (F1 generation) will be heterozygous for both traits:
- F1 Genotype: TtYy

### Step 4: Self-Cross the F1 Generation
Next, we perform a self-cross of the F1 generation (TtYy x TtYy). This will give us a 16-box Punnett square, which represents all possible combinations of the alleles.

### Step 5: Analyze the Punnett Square
The phenotypic ratio from the dihybrid cross is:
- 9 Tall Yellow (dominant for both traits)
- 3 Tall Green (dominant for height, recessive for color)
- 3 Dwarf Yellow (recessive for height, dominant for color)
- 1 Dwarf Green (recessive for both traits)

### Step 6: Identify Homozygous Dominant Plants
Homozygous dominant for both traits means having both dominant alleles:
- Homozygous Tall Yellow: TTYY

In the F2 generation, the only homozygous dominant combination (TTYY) appears in the Punnett square.

### Step 7: Calculate the Ratio
From the Punnett square, we can see that:
- There is 1 TTYY out of 16 total combinations.

Thus, the ratio of homozygous plants for both dominant characters in the F1 generation is:
- **1/16**

### Final Answer
The ratio of homozygous plants for both dominant characters in the F1 generation of a dihybrid cross is **1/16**.

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