Define heterosis.

Explanation

### Step-by-Step Solution:

1. **Introduction to Heterosis**: Heterosis, also known as hybrid vigor, refers to the phenomenon observed in hybrid organisms.

2. **Characteristics of Heterosis**: It is characterized by an increase in various traits such as size, growth rate, fertility, and yield compared to the parent organisms.

3. **Comparison with Parent Organisms**: The hybrid organism exhibits superior qualities, meaning that its characteristics are better than those of its parents.

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