Primers are
1) chemically synthesised oligonucleotides that are complementary to the regions of DNA
2) chemically synthesised oligonucleotides that are not complementary to the regions of DNA
3) chemically synthesised, autonomously replicating circular DNA molecules
4) specific sequences present on recombinant DNA

Options

A. 1) chemically synthesised oligonucleotides that are complementary to the regions of DNA
B. 2) chemically synthesised oligonucleotides that are not complementary to the regions of DNA
C. 3) chemically synthesised, autonomously replicating circular DNA molecules
D. 4) specific sequences present on recombinant DNA

Explanation

To solve the question regarding what primers are, we can break down the information as follows:

### Step-by-Step Solution:

1. **Understanding Primers**: Primers are short strands of DNA, which are also referred to as oligonucleotides. They are essential components in various molecular biology techniques, particularly in the polymerase chain reaction (PCR).

2. **Complementarity**: Primers are designed to be complementary to specific regions of the target DNA. This means that they have sequences that can base-pair with the DNA strands they are intended to amplify.

3. **Function in PCR**: During the PCR process, after the DNA has been denatured (separated into single strands), the primers anneal (bind) to their complementary sequences on the single-stranded DNA. This is crucial for the subsequent steps of DNA replication, as the primers provide a starting point for DNA polymerase to extend and synthesize new DNA strands.

4. **Evaluating Options**:
- **Option 1**: "Chemically synthesised oligonucleotides that are complementary to the regions of DNA." - This is correct as it accurately describes primers.
- **Option 2**: "Chemically synthesised oligonucleotides that are not complementary to the regions of DNA." - This is incorrect because primers must be complementary to bind effectively.
- **Option 3**: "Chemically synthesised, autonomously replicating circular DNA molecules." - This describes plasmids, not primers, so it is incorrect.
- **Option 4**: "Specific sequences present on recombinant DNA." - This refers to restriction sites, not primers, making it incorrect.

5. **Conclusion**: The correct answer is **Option 1**: "Chemically synthesised oligonucleotides that are complementary to the regions of DNA."