Question

A cross between a blue fish with the genotype Bb (dominant allele) and a white fish with the genotype bb (recessive allele) produces offspring with white scales. Which option correctly illustrates this genetic cross?

Answer 1

To illustrate the genetic cross between a blue fish with the genotype Bb (where B is the dominant allele for blue scales and b is the recessive allele for white scales) and a white fish with the genotype bb, we can use a Punnett square.

1. **Parent Genotypes:**
- Blue fish (Bb)
- White fish (bb)

2. **Gametes:**
- The blue fish can contribute either B or b.
- The white fish can only contribute b.

3. **Punnett Square:**

```
| b | b |
-------------------
B | Bb | Bb |
-------------------
b | bb | bb |
```

4. **Offspring Genotypes:**
- Bb (blue scales): 2 out of 4, or 50%
- bb (white scales): 2 out of 4, or 50%

5. **Phenotypes:**
- 50% offspring with blue scales (Bb)
- 50% offspring with white scales (bb)

From this cross, only the bb offspring will have white scales, confirming that they inherit the recessive allele from both parents.