Mark the incorrect pair (w.r.t sex determination)

Options

A. ZW-ZZ type - Fisjes
B. ZO-ZZ type - Birds
C. XX-XO type - Dioscorea
D. XX-XY type - Melandrium

Answer

To determine the incorrect pair with respect to sex determination, let's analyze the options provided:

1. **Identify the sex determination systems**:
- ZW/ZZ: In this system, males are ZZ (homogametic) and females are ZW (heterogametic). This is observed in some fish, certain amphibians, and some insects.
- ZO/ZZ: In this system, males are ZZ (homogametic) and females are ZO (where O represents the absence of a sex chromosome). This is not typical for fish, as fish generally exhibit the ZW/ZZ system.
- XO/XX: In this system, males are XO (where O represents the absence of a sex chromosome) and females are XX. This system is observed in some organisms, including humans.

2. **Evaluate each option**:
- **Option A (ZW, ZZ in fish)**: This is correct. Fish exhibit ZW/ZZ sex determination.
- **Option B (ZO, ZZ in fish)**: This is incorrect. Fish do not typically exhibit ZO/ZZ sex determination; they follow the ZW/ZZ system.
- **Option C (XO, XX in Dioscorias)**: This is correct. The XO/XX system is observed in some organisms, including humans.
- **Option D (XX, XY in humans)**: This is also correct. Humans have an XY sex determination system where males are XY and females are XX.

3. **Conclusion**: The incorrect pair with respect to sex determination is **Option B (ZO, ZZ in fish)**.

### Step-by-step solution:
1. Identify the sex determination systems: ZW/ZZ, ZO/ZZ, XO/XX, and XX/XY.
2. Evaluate each option against known biological facts.
3. Conclude that the incorrect pair is Option B (ZO, ZZ in fish).