When two hybrids rrTt and Rrtt are crossed, the phenotypic ratio of offspring would be

Options

A. `3:1`
B. `9:3:3:1`
C. `1:1`
D. ` 1:1:1:1 `

Answer

To solve the problem of determining the phenotypic ratio of the offspring from the cross between two hybrids \( rrTt \) and \( Rrtt \), we can follow these steps:

### Step 1: Identify the Parent Genotypes
The parent genotypes are:
- Parent 1: \( rrTt \) (homozygous recessive for 'r' and heterozygous for 'T')
- Parent 2: \( Rrtt \) (heterozygous for 'R' and homozygous recessive for 't')

### Step 2: Determine the Gametes
Next, we need to determine the possible gametes that each parent can produce:
- For \( rrTt \):
- Possible gametes: \( rT \) and \( rt \)

- For \( Rrtt \):
- Possible gametes: \( Rt \) and \( rt \)

### Step 3: Set Up a Punnett Square
Now we will set up a Punnett square to visualize the crosses between the gametes.

| | \( Rt \) | \( rt \) |
|--------|----------|----------|
| \( rT \) | \( RrTt \) | \( rrTt \) |
| \( rt \) | \( Rrtt \) | \( rrtt \) |

### Step 4: List the Offspring Genotypes
From the Punnett square, we can list the resulting genotypes of the offspring:
1. \( RrTt \)
2. \( rrTt \)
3. \( Rrtt \)
4. \( rrtt \)

### Step 5: Determine the Phenotypes
Now we will analyze the genotypes to determine their corresponding phenotypes:
- \( RrTt \): Dominant for 'R' and dominant for 'T' (Phenotype: Dominant)
- \( rrTt \): Recessive for 'r' and dominant for 'T' (Phenotype: Dominant)
- \( Rrtt \): Dominant for 'R' and recessive for 't' (Phenotype: Recessive)
- \( rrtt \): Recessive for both traits (Phenotype: Recessive)

### Step 6: Count the Phenotypes
Now we can count the phenotypes:
- Dominant phenotype: 2 (from \( RrTt \) and \( rrTt \))
- Recessive phenotype: 2 (from \( Rrtt \) and \( rrtt \))

### Step 7: Calculate the Phenotypic Ratio
The phenotypic ratio of the offspring is:
- Dominant : Recessive = 2 : 2 = 1 : 1

### Final Answer
The phenotypic ratio of the offspring when \( rrTt \) is crossed with \( Rrtt \) is **1:1**.

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