Male heterogamety is absent in

Options

A. birds
B. human
C. roundworm
D. Drosophila

Answer

**Step-by-Step Solution:**

1. **Understanding Male Heterogamety**:
- Male heterogamety refers to the condition where males produce two different types of gametes. In humans and Drosophila (fruit flies), males have one X chromosome and one Y chromosome (XY), which allows them to produce two types of gametes: one carrying the X chromosome and the other carrying the Y chromosome.

2. **Analyzing the Options**:
- **Birds**: In birds, males have two Z chromosomes (ZZ), and females have one Z and one W chromosome (ZW). Since males do not produce different types of gametes, male heterogamety is absent in birds.
- **Humans**: In humans, males have one X and one Y chromosome (XY), hence they exhibit male heterogamety.
- **Roundworms**: In roundworms, males typically have one X chromosome and no second sex chromosome (XO). This means they also produce only one type of gamete, indicating that male heterogamety is absent.
- **Drosophila**: In Drosophila, males have one X and one Y chromosome (XY), which means they exhibit male heterogamety.

3. **Conclusion**:
- From the analysis, we see that male heterogamety is absent in birds and roundworms. However, since the question asks for the absence of male heterogamety, the best answer is **birds**.

**Final Answer**: Male heterogamety is absent in **birds**.

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