In metamale Drosophila, chromosome combination is:

Options

A. 3X: 2A
B. 3X: 3A
C. XY: 3A
D. XY: 2A

Answer

To determine the chromosome combination in metamale Drosophila, we need to analyze the X chromosome to autosome ratio. Here’s a step-by-step solution:

### Step 1: Understand the Chromosome Composition
Drosophila has sex chromosomes (X and Y) and autosomes. The sex of Drosophila is determined primarily by the number of X chromosomes relative to the number of sets of autosomes.

**Hint:** Remember that in Drosophila, the presence of X chromosomes is more critical than the presence of Y chromosomes in determining sex.

### Step 2: Determine the Ratios
The sex determination in Drosophila is based on the X chromosome to autosome ratio (X:A). The following ratios are significant:
- **Ratio of 1**: Female
- **Ratio of 0.5**: Male
- **Ratio less than 0.5**: Metamale
- **Ratio greater than 1**: Metafemale
- **Ratio between 0.5 and 1**: Intersex

**Hint:** Focus on the numerical values of the X:A ratio to classify the sex type.

### Step 3: Analyze the Given Combinations
We need to evaluate the combinations of X chromosomes and autosomes to find the metamale condition:
1. **Combination 1**: X = 3, A = 2 → Ratio = 3/2 = 1.5 (Metafemale)
2. **Combination 2**: X = 3, A = 3 → Ratio = 3/3 = 1 (Female)
3. **Combination 3**: X = 1, A = 3 → Ratio = 1/3 ≈ 0.33 (Metamale)
4. **Combination 4**: X = 1, A = 2 → Ratio = 1/2 = 0.5 (Normal Male)

**Hint:** Calculate the ratio for each combination to identify which one corresponds to metamale.

### Step 4: Identify the Metamale Condition
From the analysis, we see that the third combination (X = 1, A = 3) gives a ratio of approximately 0.33, which fits the criteria for a metamale.

**Hint:** Look for the combination where the X:A ratio is less than 0.5 to confirm the metamale classification.

### Conclusion
The chromosome combination that results in a metamale Drosophila is when there is 1 X chromosome and 3 autosomes, leading to an X:A ratio of approximately 0.33.

**Final Answer:** The chromosome combination for metamale Drosophila is X = 1 and A = 3.