When two unrelated individuals or lines are crossed, the performance of `F_(1)` hybrids is often superior to both its parents. The phenomenon is called

Options

A. heterosis
B. transformation
C. splicing
D. metamorphosis

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question states that when two unrelated individuals or lines are crossed, the performance of the resulting F1 hybrids is often superior to that of both parents. We need to identify the term that describes this phenomenon.

2. **Identifying Key Terms**: The key terms in the question are "unrelated individuals," "crossed," "F1 hybrids," and "superior performance." This indicates that we are looking for a genetic concept related to hybrid vigor.

3. **Evaluating the Options**:
- **Option 1: Heterosis**: This term refers to the phenomenon where the offspring (F1 hybrids) exhibit greater biomass, growth rate, and yield compared to their parents. This is often observed in hybrid plants and animals.
- **Option 2: Transformation**: This refers to the genetic alteration of a cell by the uptake of foreign DNA, which is not relevant to the context of hybrid vigor.
- **Option 3: Splicing**: This is a molecular biology process involving the removal of introns from RNA, which does not relate to hybrid performance.
- **Option 4: Metamorphosis**: This term describes the transformation from a larval stage to an adult form in certain organisms, which is unrelated to the concept of hybrid vigor.

4. **Conclusion**: Given the definitions and relevance of each option, the correct answer to the question is **Heterosis**. Heterosis explains the increased vigor and performance of F1 hybrids compared to their parents.

### Final Answer:
The phenomenon is called **Heterosis**.

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