Cross between homozygous black rough (BBRR) guinea pig and homozygous white smooth guinea pig (bbrr) produced black and rough animals in `F_(1)` generation. Presuming the genes to be present on different chromosomes, the percentage of `F_(2)` individuals which are heterozygous for both the gene pairs would be

Options

A. 0.25
B. 0.35
C. 0.5
D. 0.75

Answer

To solve the problem, we will follow these steps:

### Step 1: Identify the Parent Genotypes
The problem states that we have two homozygous guinea pigs:
- One is homozygous black rough (BBRR).
- The other is homozygous white smooth (bbrr).

### Step 2: Determine the F1 Generation
When these two guinea pigs are crossed, the F1 generation will be heterozygous for both traits:
- All F1 offspring will have the genotype BbRr, which means they will be black and rough.

### Step 3: Set Up the F2 Generation
To find the F2 generation, we need to self-cross the F1 individuals (BbRr x BbRr).

### Step 4: Use a Punnett Square
We can use a Punnett square to determine the genotypes of the F2 generation. Since we are dealing with two traits, we will create a 4x4 Punnett square:

| | BR | Br | bR | br |
|-----|----|----|----|----|
| **BR** | BBRR | BBRr | BbRR | BbRr |
| **Br** | BBRr | BBrr | BbRr | BbrR |
| **bR** | BbRR | BbRr | bbRR | bbRr |
| **br** | BbRr | BbrR | bbRr | bbrr |

### Step 5: Count the Heterozygous Individuals
From the Punnett square, we can identify the genotypes:
- The heterozygous individuals for both traits (BbRr) appear in the following combinations:
- BbRr (occurs 4 times)

### Step 6: Calculate the Total Number of Offspring
In total, there are 16 possible combinations (4 rows x 4 columns).

### Step 7: Calculate the Percentage of Heterozygous Individuals
To find the percentage of F2 individuals that are heterozygous for both gene pairs (BbRr):
- There are 4 BbRr out of 16 total offspring.
- Therefore, the percentage is (4/16) * 100 = 25%.

### Conclusion
The percentage of F2 individuals that are heterozygous for both gene pairs is **25%** or **0.25**.

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