A rooster with gray feathers was mated with a hen of same phenotype. Among their offspring 15 were gray, 6 black and 8 white. What phenotypes would you expect among the offspring resulting from mating of gray rooster and black hen ?

Options

A. all black
B. all gray
C. Equal proportion of black and gray
D. 1/4gray and 3/4 black

Answer

To solve the problem, we need to analyze the genetic inheritance of feather color in roosters and hens. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand the Inheritance Pattern
The feather color in roosters is determined by incomplete dominance. This means that when two different alleles are present, the phenotype is a blend of both traits. We can denote the alleles as follows:
- **B**: Black feathers (dominant)
- **b**: White feathers (recessive)
- **Bb**: Gray feathers (incomplete dominance)

### Step 2: Analyze the Offspring from the First Cross
From the initial mating of a gray rooster (Bb) with a gray hen (Bb), the offspring phenotypes were:
- Gray: 15
- Black: 6
- White: 8

To find the expected genotypic ratio, we can set up a Punnett square for the Bb x Bb cross:
- BB (Black)
- Bb (Gray)
- bb (White)

The expected ratio from this cross is:
- 1 BB : 2 Bb : 1 bb, which translates to 1 Black : 2 Gray : 1 White.

### Step 3: Calculate the Total Offspring
Total offspring = 15 (Gray) + 6 (Black) + 8 (White) = 29.

### Step 4: Determine the Expected Ratio
From the observed offspring, we can calculate the expected ratios:
- Gray (Bb) = 15
- Black (BB) = 6
- White (bb) = 8

### Step 5: Predict the Offspring from the New Cross
Now, we need to determine the expected phenotypes when a gray rooster (Bb) is mated with a black hen (BB):
- The possible gametes from the gray rooster (Bb) are B and b.
- The possible gametes from the black hen (BB) are B and B.

Using a Punnett square for this cross:
```
B B
----------------
B | BB | BB |
----------------
b | Bb | Bb |
----------------
```

### Step 6: Determine the Expected Phenotypes
From the Punnett square:
- BB (Black) = 2
- Bb (Gray) = 2

Thus, the expected phenotypic ratio is:
- 2 Black : 2 Gray, which simplifies to 1 Black : 1 Gray.

### Conclusion
When a gray rooster (Bb) is mated with a black hen (BB), we expect the offspring to be in a 1:1 ratio of black to gray feathers.

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