In birds

Options

A. Females have heteromorphic sex chromosomes
B. Males have heteromorphic sex chromosomes
C. Females have isomorphic sex chromosomes
D. Males have XO/ZO chromosome complement

Answer

To solve the question regarding the sex chromosomes in birds, we need to understand the chromosomal basis of sex determination in these organisms. Here’s a step-by-step breakdown of the solution:

### Step-by-Step Solution:

1. **Understanding Bird Sex Chromosomes**:
- In birds, the sex determination system is known as the ZW system. Males have two Z chromosomes (ZZ), while females have one Z and one W chromosome (ZW).

2. **Identifying Male Chromosomes**:
- Male birds have a homomorphic pair of sex chromosomes (ZZ). This means both chromosomes are of the same type, and they can only produce one type of gamete, which is Z.

3. **Identifying Female Chromosomes**:
- Female birds have heteromorphic sex chromosomes (ZW). This means the two chromosomes are different from each other, allowing females to produce two types of gametes: Z and W.

4. **Evaluating the Options**:
- **Option A**: "Females have heteromorphic sex chromosomes" - This is correct (ZW).
- **Option B**: "Males have heteromorphic sex chromosomes" - This is incorrect (ZZ is homomorphic).
- **Option C**: "Females have isomorphic sex chromosomes" - This is incorrect (females have ZW, which are not isomorphic).
- **Option D**: "Males have exo-zero chromosome complement" - This is incorrect (males have ZZ).

5. **Conclusion**:
- The only correct statement is that females have heteromorphic sex chromosomes (ZW). Therefore, the correct answer is Option A.