For The First Time, Scientists Have Completely Sequenced a Human Chromosome
In 2003, history was made. For the first time, the human genome was sequenced. Since then, technological improvements have enabled tweaks, adjustments, and additions, making the human genome the most accurate and complete vertebrate genome ever sequenced.
Nevertheless, some gaps remain - including human chromosomes. We have a pretty good grasp of them in general, but there are still some gaps in the sequences. Now, for the first time, geneticists have closed some of those gaps, giving us the first complete, gap-free, end-to-end (or telomere-to-telomere) sequence of a human X chromosome.
The accomplishment was enabled by a new technique called nanopore sequencing, which enables ultra-long-reads of DNA strands, providing a more complete and sequential assembly.
This is in contrast to previous sequencing techniques, in which only short sections could be read at a time. Previously, geneticists had to piece together these sections like a puzzle.
While they were pretty good at this, the pieces tend to look the same, so it's very tricky to know if you're getting it right - not just the right order, but how many repeats there are in the sequence. And, of course, there are minute gaps.
This is where nanopore sequencing comes in. It consists of a protein nanopore - a nanoscale hole - set in an electrically resistant membrane. Current is applied to the membrane, which passes it through the nanopore. When genetic material is fed into the nanopore, the change in current can be translated into a genetic sequence.
Even better, this technology reduces reliance on polymerase chain reaction, a technique that amplifies DNA by creating millions of copies of it.