Mark the incorrect pair (w.r.t sex determination)
(a) ZW-ZZ type - Fishes
(b) ZO-ZZ type - Birds
(c) XX-XO type - Dioscorea
(d) XX-XY type - Melandrium

Options

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

Answer

To solve the question of identifying the incorrect pair with respect to sex determination, we will analyze each option one by one.

### Step-by-Step Solution:

1. **Analyze Option A: ZW-ZZ type - Fishes**
- In the ZW-ZZ sex determination system, the ZW represents the female (heterogametic) and ZZ represents the male (homogametic). This system is indeed observed in some fish species, as well as in birds and butterflies.
- **Conclusion:** This pair is correct.

2. **Analyze Option B: ZO-ZZ type - Birds**
- The ZO-ZZ sex determination system is not typical for birds. Birds generally exhibit the ZW-ZZ system, where females are ZW and males are ZZ. The ZO-ZZ system is more commonly associated with certain insects, not birds.
- **Conclusion:** This pair is incorrect.

3. **Analyze Option C: XX-XO type - Dioscorea**
- The XX-XO sex determination system is observed in some plants, including Dioscorea (yam). In this system, females are XX and males are XO.
- **Conclusion:** This pair is correct.

4. **Analyze Option D: XX-XY type - Melandrium**
- The XX-XY sex determination system is present in Melandrium, where females are XX and males are XY. This is a well-documented system in many organisms, including plants.
- **Conclusion:** This pair is correct.

### Final Answer:
The incorrect pair regarding sex determination is **(b) ZO-ZZ type - Birds**.