cDNA is

Options

A. Circular DNA in bacteria
B. Complementary DNA
C. Copy DNA
D. Both (2) and (3)

Answer

**Step-by-Step Solution:**

1. **Understanding cDNA**: cDNA stands for complementary DNA. It is a form of DNA that is synthesized from a single-stranded RNA template, typically messenger RNA (mRNA).

2. **Synthesis of cDNA**: The process of synthesizing cDNA involves an enzyme called reverse transcriptase. This enzyme converts the RNA sequence back into DNA, allowing researchers to obtain the genetic information encoded in the RNA.

3. **Applications of cDNA**: cDNA is primarily used in molecular biology for cloning eukaryotic genes in prokaryotic organisms. This is particularly useful when studying gene expression and function.

4. **Evaluating the Options**:
- **Option 1**: Circular DNA in bacteria - This refers to the natural form of bacterial DNA, which is indeed circular, but it is not what cDNA stands for.
- **Option 2**: Complementary DNA - This is correct, as cDNA is indeed complementary DNA.
- **Option 3**: Copy DNA - This term is not commonly used in genetics and is incorrect in this context.
- **Option 4**: Both two and three - Since option three is incorrect, this option is also incorrect.

5. **Conclusion**: The correct answer is that cDNA stands for complementary DNA.

**Final Answer**: cDNA is complementary DNA.

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