To solve the question "YAC" refers to, we can follow these steps:
### Step-by-Step Solution:
1. **Identify the Acronym**: Start by breaking down the acronym YAC. It consists of three letters: Y, A, and C.
2. **Determine the Meaning of Each Letter**:
- The letter **Y** stands for **Yeast**.
- The letter **A** stands for **Artificial**.
- The letter **C** stands for **Chromosome**.
3. **Combine the Meanings**: When we combine the meanings of each letter, we get "Yeast Artificial Chromosome".
4. **Understand the Context**: Recognize that YAC is a term used in genetic engineering. It refers to a vector that can carry large fragments of DNA for cloning purposes.
5. **Confirm the Answer**: Given the options provided:
- Yeast Artificial
- Yeast Artificial Chromosome
- Yeast Artificial Colony
- None of these
The correct full form of YAC is **Yeast Artificial Chromosome**.
### Final Answer:
YAC refers to **Yeast Artificial Chromosome**.
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