This method of finding a gene is used when researchers know very little about the gene they are trying to find. This process results in a complete gene library: a collection of copies of DNA fragments that represent the entire genome of an organism.

Options

A. Cloning
B. Shotgun cloning
C. Gene synthesis cloning
D. PCR

Answer

To solve the question regarding the method of finding a gene when researchers have limited information, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: The question describes a method for finding a gene when there is little prior knowledge about it. It also mentions that this process results in a complete gene library, which is a collection of DNA fragments representing the entire genome of an organism.

2. **Analyze the Options**: The options provided are:
- Cloning
- Shotgun cloning
- Gene synthesis cloning
- PCR (Polymerase Chain Reaction)

3. **Evaluate Each Option**:
- **Cloning**: This generally refers to the process of creating identical copies of a cell or organism. It does not specifically relate to generating a complete gene library.
- **Shotgun Cloning**: This technique involves randomly breaking up DNA and then cloning the fragments. It can lead to a gene library but is not as efficient in generating a complete representation of the genome as other methods.
- **Gene Synthesis Cloning**: This method involves synthesizing genes from scratch based on known sequences. It is not applicable when researchers know very little about the gene.
- **PCR (Polymerase Chain Reaction)**: This method is used to amplify specific DNA sequences. It can be used to create a complete gene library by amplifying fragments of DNA from the entire genome.

4. **Identify the Correct Answer**: Given that the question specifies the creation of a complete gene library and that researchers know very little about the gene, the most appropriate method is PCR. PCR allows for the amplification of DNA fragments, which can then be used to construct a complete gene library.

5. **Final Conclusion**: The correct answer to the question is **PCR (Polymerase Chain Reaction)**.