The allele for pea comb (P) in chickens is completely dominant to the allele for single comb (p) . The alleles for black feather colour (B), and white feather colour (B') show codominance, so that BB' individuals possess blue feathers. If chickens heterozygous for both pairs of genes are mated what proportion of offspring are expected to be pea combed and white feathered ?

Options

A. `9//16`
B. `3//16`
C. `1//16`
D. `2//16`

Answer

To solve the problem, we need to determine the proportion of offspring that are pea-combed (P) and white-feathered (B') when chickens heterozygous for both traits are mated. Here’s a step-by-step breakdown of the solution:

### Step 1: Identify the Genotypes of the Parents
The parents are heterozygous for both traits:
- For comb type: Pp (pea comb)
- For feather color: Bb' (black and white feather color)

Thus, the genotype of each parent is PpBb'.

### Step 2: Determine the Gametes
Each parent can produce gametes based on their genotype. The gametes produced by each parent can be determined using the FOIL method (First, Outside, Inside, Last):
- Possible gametes from PpBb' are: PB, Pb, pB, pb.

### Step 3: Set Up a Punnett Square
We will set up a Punnett square to find the possible combinations of the offspring. Since both parents can produce four types of gametes, we will create a 4x4 Punnett square.

| | PB | Pb | pB | pb |
|---------|----------|----------|----------|----------|
| **PB** | PPBB' | PPbB' | PpBB' | PpBb' |
| **Pb** | PPBb' | PPbb' | PpBb' | Ppbb' |
| **pB** | PpBB' | PpBb' | ppBB' | ppBb' |
| **pb** | PpBb' | Ppbb' | ppBb' | ppbb' |

### Step 4: Count the Desired Offspring
We are interested in offspring that are:
- Pea-combed (P) - which includes genotypes PP or Pp.
- White-feathered (B') - which includes genotype Bb'.

Now, we will count the offspring that meet these criteria:
- From the Punnett square:
- PPBB' (1)
- PPbB' (1)
- PpBB' (2)
- PpBb' (4)

Total offspring that are pea-combed and white-feathered:
- PPBB' (1)
- PPbB' (1)
- PpBB' (2)
- PpBb' (4)

Total = 1 + 1 + 2 + 4 = 8

### Step 5: Calculate the Total Offspring
The total number of offspring in the Punnett square is 16 (4x4).

### Step 6: Calculate the Proportion
To find the proportion of offspring that are pea-combed and white-feathered:
- Proportion = Number of desired offspring / Total offspring = 8 / 16 = 1/2.

### Final Answer
The proportion of offspring expected to be pea-combed and white-feathered is **1/2**.

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