If four o' clock plants, the gene for red flower colour (R) is incompletely dominant over the gene for white flower colour (r), hence the plants heterozygous for flower colour (Rr) have pink flower. What will be the ratio of offsprings in a cross between the red flowers and pink flowers ?

Options

A. `75 %` red flower, `25 %` pink flowers
B. All red flowers
C. `50 %` red flowers, `50 %` pink flowers
D. Red : pink : white :: 1 : 2 : 1

Explanation

To solve the problem of determining the ratio of offspring in a cross between red-flowered (RR) and pink-flowered (Rr) four o'clock plants, we will follow these steps:

### Step 1: Identify the Genotypes
- Red flower color is represented by the genotype **RR** (homozygous).
- Pink flower color is represented by the genotype **Rr** (heterozygous).

### Step 2: Determine the Gametes
- The red-flowered plant (RR) can produce only one type of gamete: **R**.
- The pink-flowered plant (Rr) can produce two types of gametes: **R** and **r**.

### Step 3: Set Up the Punnett Square
- We will set up a Punnett square to visualize the cross between the gametes of the two parent plants:

| | R (from RR) | R (from Rr) |
|-----|--------------|--------------|
| **R (from RR)** | RR | RR |
| **r (from Rr)** | Rr | Rr |

### Step 4: Fill in the Punnett Square
- The combinations from the Punnett square will be:
- RR (Red)
- RR (Red)
- Rr (Pink)
- Rr (Pink)

### Step 5: Analyze the Results
- From the Punnett square, we can see the following phenotypes:
- 2 RR (Red)
- 2 Rr (Pink)

### Step 6: Calculate the Ratio
- The ratio of the offspring is:
- Red flowers (RR): 2
- Pink flowers (Rr): 2
- Therefore, the ratio of red to pink flowers is **1:1**.

### Final Answer
The ratio of offspring in a cross between red flowers (RR) and pink flowers (Rr) is **1:1**.

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