Small chemically synthesised oligonucleotides that are complementary to the regions of DNA are called primers and present at the ....

Options

A. 5' end
B. 3' end
C. Both 3' and 5' end
D. None of the above

Explanation

**Step-by-Step Solution:**

1. **Identify the Definition of Primers**: Small chemically synthesized oligonucleotides that are complementary to specific regions of DNA are known as primers.

2. **Understand the Nature of Primers**: Primers can be either short DNA or RNA molecules. They are specifically designed to bind to a target sequence of DNA.

3. **Recognize the Role of Primers**: Primers play a crucial role in various applications, particularly in genetic testing, research, and forensic science. They are essential for processes like PCR (Polymerase Chain Reaction), where they initiate the replication of a specific DNA segment.

4. **Define Oligonucleotides**: The term "oligonucleotide" refers to a short sequence of nucleotide residues. These sequences are typically made up of 20-30 nucleotides and are synthesized to be complementary to the target DNA sequence.

5. **Summarize the Importance of Primers**: In summary, primers are vital tools in molecular biology that facilitate the amplification and analysis of DNA, making them indispensable in genetic testing and other scientific research.