The Next Generation Sequencing (NGS) allows to sequence the whole genome of an
organism, compared to Maxam and Gilbert and Sanger sequencing that only allow to
sequence, hardly, a single gene. Removing the separation of DNA fragments by
electrophoresis, and the development of techniques that let the parallelization (analysing
simultaneously several DNA fragments) have been crucial for the improvements of this
process. The new companies in this ambit, Roche and Illumina, bet for different protocols to
achieve these goals. Illumina bets for the sequencing by synthesis (SBS), requiring the library
preparation and the use of adapters. Likewise, Illumina has replaced Roche because its lower
rate of misincorporation, making it ideal for studies of genetic variability, transcriptomic,
epigenomic, and metagenomic, in which this study will focus.
However, it is noteworthy that the last progress in sequencing is carried out by the third
generation sequencing, using nanotechnology to design small sequencers that sequence the
whole genome of an organism quickly and inexpensively. Moreover, they provide more
reliable data than current systems because they sequence a single molecule, solving the
problem of synchronisation. In this way, PacBio and Nanopore allow a great progress in
diagnostic and personalized medicine.
Metagenomics provide to make a qualitative and quantitative analysis of the various species
present in a sample. The main advantage of this technique is the no necessary isolation and
growth of the species, allowing the analysis of nonculturable species. The Illumina protocol
studies the variable regions of the 16S rRNA gene, which contains variable and not variables
regions providing a phylogenetic classification. Therefore, metagenomics is a topic of
interest to know the biodiversity of complex ecosystems and to study the microbiome of
patients given the high involvement with certain microbial profiles on the condition of
certain metabolic diseases.
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