![]() The DNA sequence is analysed base-by-base during Illumina sequencing, making it a highly accurate method.And so the process continues until millions of clusters have been sequenced. The fluorescently-labelled terminator group is then removed from the first base and the next fluorescently-labelled terminator base can be added alongside.Each of the terminator bases (A, C, G and T) give off a different colour. This fluorescence is detected by a camera and recorded on a computer. Lasers are passed over the flowcell to activate the fluorescent label on the nucleotide base.Once a base has been added no more bases can be added to the strand of DNA until the terminator base is cut from the DNA. The DNA polymerase then binds to the primer and adds the first fluorescently-labelled terminator to the new DNA strand.The primer attaches to the DNA being sequenced.Primers and fluorescently-labelled terminators (terminators are a version of nucleotide base – A, C, G or T – that stop DNA synthesis) are added to the flowcell.The double-stranded DNA is then broken down into single-stranded DNA using heat, leaving several million dense clusters of identical DNA sequences.This creates ‘bridges’ of double-stranded DNA between the primers on the flowcell surface. Unlabelled nucleotide bases and DNA polymerase are then added to lengthen and join the strands of DNA attached to the flowcell.When sequenced, each cluster of DNA molecules will emit a signal that is strong enough to be detected by a camera. The DNA attached to the flowcell is then replicated to form small clusters of DNA with the same sequence. ![]() The complementary DNA binds to primers on the surface of the flowcell and DNA that doesn’t attach is washed away.
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