If dominant C and P genes are essential for the development of purple colour in Lathyrus odoratus flowers. What would be the ratio of purple and white colour in a cross between CcPp xcc Pp.

Options

A. `3:5`
B. `9:7`
C. `2:6`
D. `4:4`

Answer

To solve the problem of determining the ratio of purple to white flowers in a cross between CcPp (heterozygous for both traits) and ccPp (homozygous recessive for the C gene and heterozygous for the P gene), we can follow these steps:

### Step 1: Determine the Gametes
1. **For CcPp (parent 1)**: The possible gametes are:
- CP (dominant C and dominant P)
- Cp (dominant C and recessive p)
- cP (recessive c and dominant P)
- cp (recessive c and recessive p)

2. **For ccPp (parent 2)**: The possible gametes are:
- cP (recessive c and dominant P)
- cp (recessive c and recessive p)

### Step 2: Set Up the Punnett Square
Now we can set up a Punnett square using the gametes from both parents:

| | cP | cp |
|---------|----------|----------|
| **CP** | CcPp | Ccpp |
| **Cp** | CcPp | Ccpp |
| **cP** | ccPp | ccpp |
| **cp** | ccPp | ccpp |

### Step 3: Determine the Genotypes
From the Punnett square, we can determine the genotypes of the offspring:
1. **CcPp** - Purple (dominant C and dominant P)
2. **Ccpp** - White (dominant C is absent)
3. **ccPp** - White (recessive c is present)
4. **ccpp** - White (both recessive alleles are present)

### Step 4: Count the Phenotypes
Now, we can count the number of purple and white flowers:
- **Purple flowers (CcPp)**: 2
- **White flowers (Ccpp, ccPp, ccpp)**: 6

### Step 5: Calculate the Ratio
The ratio of purple to white flowers is:
- Purple: 2
- White: 6

Thus, the ratio of purple to white flowers is **2:6**, which simplifies to **1:3**.

### Final Answer
The ratio of purple to white flowers in the cross between CcPp and ccPp is **1:3**.

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