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HiSeq & MiSeq
The HiSeq and MiSeq use a green laser to sequence G/T and a red laser to sequence A/C. At each cycle at least one of two nucleotides for each color channel must be read to ensure proper registration. It is important to maintain color balance for each base of the index read being sequenced, otherwise index read sequencing could fail due to registration failure. E.g. if the sample contains only T and C in the first four cycles, image registration will fail. (If possible spike-in phiX sequence to add diversity to low-plex sequencing libraries.)
If one or more bases are not present in the first 11 cycles the quality of the run will be negatively impacted. This is because the color matrix is calculated from the color signals of these cycles.
The NextSeq 500 uses two-channel sequencing, which requires only two images to encode the data for four DNA bases, one red channel and one green channel. The NextSeq also uses a new implementation of real-time analysis (RTA) called RTA2.0, which includes important architecture differences from RTA on other Illumina sequencers. For any index sequences, RTA2.0 requires that there is at least one base other than G in the first two cycles. This requirement for index diversity allows the use of any Illumina index selection for single-plex indexing except index 1 (i7) 705, which uses the sequence GGACTCCT. Use the combinations in the table below for proper color balancing on the NextSeq 500.
This entry was posted on 04 Nov 2014 at 22:42 by and is filed under Sequencing.