An example of gene therapy is

Options

A. Production of injectable hepatitis B vaccine
B. Production of vaccines in food crops like potatoes which can be eaten
C. Introduction of gene for adenosine deaminase in persons suffering from Severe Combined Immuno Deficiency (SCID)
D. Production of test tube babies by artificial insemination and implantion of fertilized eggs

Answer

To solve the question "An example of gene therapy is," we need to analyze the provided options and understand the concept of gene therapy.

### Step-by-Step Solution:

1. **Understand Gene Therapy**:
- Gene therapy is a technique that modifies a person's genes to treat or prevent disease. It involves replacing, inactivating, or introducing genes into cells to correct genetic disorders.

2. **Evaluate the Options**:
- **Option 1**: Production of injectable hepatitis B vaccine.
- This is related to vaccine production, not gene therapy.
- **Option 2**: Production of vaccines in food crops like potatoes.
- This refers to genetically modified organisms (GMOs), not gene therapy.
- **Option 3**: Introduction of gene for adenosine deaminase in persons suffering from severe combined immunodeficiency (SCID).
- This directly relates to gene therapy, as it involves correcting a genetic defect.
- **Option 4**: Production of test tube babies by artificial insemination and implantation of fertilized eggs.
- This is a reproductive technology, not gene therapy.

3. **Identify the Correct Answer**:
- Among the options, **Option 3** is the only one that describes a process of gene therapy, where the gene responsible for producing the enzyme adenosine deaminase (ADA) is introduced to treat SCID.

4. **Conclusion**:
- The correct answer to the question "An example of gene therapy is" is **Option 3: Introduction of gene for adenosine deaminase in persons suffering from severe combined immunodeficiency (SCID)**.