A polymerase chain reaction on human alphoid DNA produces a characteristic ladder of bands.

A polymerase chain reaction (PCR) was performed on the tandemly repeated human alphoid DNA sequence. A characteristic ladder of bands was produced which differed by 171 (or 340) base pairs. This laddering phenomenon occurs because the two oligonucleotides can bind within the same monomer or in neighbouring monomers. In the latter case a larger PCR product is produced which is 171 bp or a multiple of 171 base pairs greater in size. The alphoid DNA PCR is very sensitive because a repeated sequence is amplified. Hence it could have applications in archaeology or forensic science.