A primer is short oligo made from nucleic acids. It is the starting point for DNA polymerases to start DNA synthesis. DNA polymerases can only synthesize enlarge existing nucleic but not generate new ones 'de novo'. Primers can be made of DNA (for PCR) or RNA (naturally occuring).
How is primer annealing, and, consequently, PCR amplification affected by single nucleotide deletion or insertion inside the primer ? Imagine a primer like this: GCGTCATAAAGGGGACGTG (primer) and ...