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.