What are Probes, Primers, Tags and Adaptors in relation to DNA Testing?
The first two serve a similar function. That is, to find an area of DNA to analyze. Probes are the term used for microarray testing as they are placed in a specific, known area of the array. Primers are what is used in CE testing to find a specific area of DNA to then pass just that through the sequencer. Key is, both need knowledge about what marker is being sought for analysis and what the nearby DNA looks like to create the Probe or Primer to find it.
Adaptors are specific sequences of DNA artificially constructed and attached to the ends of the fragments created in preparation for NGS. They allow the DNA fragment to be attached to the flow cell / plate of the sequencer and thus hold it in place during the many cycles of analysis. Often, an identifying Tag is built into the Adaptor that is unique to a sample so multiple samples can be mixed in a single run. This way, when the sequencer starts sequencing at the end of the fragment with the Adaptor, the Adaptor sequence with the Tag will be in the result. Helping to separate and identify the results.
The 2.5 generation form of sequencing goes a step further. In that it uses additional unique Tags to group fragments that were larger before being broken up smaller. Thus allowing post-processing from the sequencer result to reconstruct the larger, initial fragments.
Adaptors and Tags are stripped from the read segments before being stored in that samples FASTQ file.
The first two serve a similar function. That is, to find an area of DNA to analyze. Probes are the term used for microarray testing as they are placed in a specific, known area of the array. Primers are what is used in CE testing to find a specific area of DNA to then pass just that through the sequencer. Key is, both need knowledge about what marker is being sought for analysis and what the nearby DNA looks like to create the Probe or Primer to find it.
Adaptors are specific sequences of DNA artificially constructed and attached to the ends of the fragments created in preparation for NGS. They allow the DNA fragment to be attached to the flow cell / plate of the sequencer and thus hold it in place during the many cycles of analysis. Often, an identifying Tag is built into the Adaptor that is unique to a sample so multiple samples can be mixed in a single run. This way, when the sequencer starts sequencing at the end of the fragment with the Adaptor, the Adaptor sequence with the Tag will be in the result. Helping to separate and identify the results.
The 2.5 generation form of sequencing goes a step further. In that it uses additional unique Tags to group fragments that were larger before being broken up smaller. Thus allowing post-processing from the sequencer result to reconstruct the larger, initial fragments.
Adaptors and Tags are stripped from the read segments before being stored in that samples FASTQ file.
External References
- Our document on Read Length and Insert Size that briefly touches on Adaptors.