Which of the following is correct about ZW - ZZ type of sex determination in birds?

Options

A. Males are heterogametic
B. Females are heterogametic
C. Females are homogametic
D. Both males and females are homogametic

Answer

To answer the question regarding ZW - ZZ type of sex determination in birds, let's break down the concept step by step.

### Step 1: Understand the ZW - ZZ System
In birds, sex determination is typically based on the ZW - ZZ system. This means:
- Males are homogametic (ZZ), having two identical sex chromosomes (ZZ).
- Females are heterogametic (ZW), having two different sex chromosomes (ZW).

### Step 2: Identify Key Characteristics
1. **Male Birds (ZZ)**:
- Males possess two Z chromosomes.
- They typically express dominant traits associated with the Z chromosome.

2. **Female Birds (ZW)**:
- Females possess one Z and one W chromosome.
- The W chromosome can carry traits that are not present in males.

### Step 3: Implications of the ZW - ZZ System
- The ZW - ZZ system is a form of chromosomal sex determination, which is different from the XY system found in mammals.
- The sex of the offspring is determined by the type of sex chromosome contributed by the mother (ZW) since the father (ZZ) can only contribute a Z chromosome.

### Step 4: Conclusion
In summary, the ZW - ZZ sex determination system in birds means that:
- Males are ZZ (homogametic) and females are ZW (heterogametic).
- The female's contribution determines the sex of the offspring.

### Final Answer
The correct statement about ZW - ZZ type of sex determination in birds is that males are ZZ and females are ZW.

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