Heterozygous tall and violet flower garden pea plants were selfed, and total 1200 plants are collected. What will be the total number of plants with first dominant and second recessive traits?

Options

A. 150
B. 675
C. 225
D. 450

Answer

To solve the problem, we need to analyze the genetic cross of heterozygous tall and violet flower garden pea plants. Let's break it down step by step.

### Step 1: Identify the Traits and Alleles
- The first trait is **stem height**:
- Dominant allele (Tall): T
- Recessive allele (Dwarf): t
- The second trait is **flower color**:
- Dominant allele (Violet): V
- Recessive allele (White): v

### Step 2: Determine the Genotypes of the Parents
Since the plants are heterozygous for both traits, the genotype of each parent plant is:
- TtVv (Tall and Violet)

### Step 3: Set Up the Dihybrid Cross
When we perform a dihybrid cross between two TtVv plants, we can use a Punnett square to determine the possible offspring genotypes. The gametes produced by each parent will be:
- TV, Tv, tV, tv

### Step 4: Create the Punnett Square
The Punnett square for this dihybrid cross will yield 16 possible combinations of the alleles:

| | TV | Tv | tV | tv |
|------|-----|-----|-----|-----|
| **TV** | TTVV | TTVv | TtVV | TtVv |
| **Tv** | TTVv | TTvv | TtVv | Ttvv |
| **tV** | TtVV | TtVv | ttVV | ttVv |
| **tv** | TtVv | Ttvv | ttVv | ttvv |

### Step 5: Determine the Phenotypes
From the Punnett square, we can categorize the phenotypes:
- **Tall and Violet (TT or Tt, VV or Vv)**: 9
- **Tall and White (TT or Tt, vv)**: 3
- **Dwarf and Violet (tt, VV or Vv)**: 3
- **Dwarf and White (tt, vv)**: 1

### Step 6: Calculate the Ratio
The phenotypic ratio of the offspring is:
- 9 Tall Violet : 3 Tall White : 3 Dwarf Violet : 1 Dwarf White

### Step 7: Find the Specific Phenotype
We are interested in the plants that are:
- **Tall (dominant trait)** and **White (recessive trait)**, which corresponds to the 3 in the ratio.

### Step 8: Calculate the Number of Plants
Given that there are a total of 1200 plants:
- The proportion of Tall White plants is \( \frac{3}{16} \).

Now, calculate the number of Tall White plants:
\[ \text{Number of Tall White plants} = \frac{3}{16} \times 1200 = 225 \]

### Final Answer
The total number of plants with the first dominant (Tall) and second recessive (White) traits is **225**.

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