You’ve likely heard of the Human Genome Project. That’s because it is one of the most ambitious scientific projects of all time. The program ended in 2003 with over 92 percent of the human genome mapped, but this week, scientists have added to the project with the complete mapping of an entire X chromosome. 

Mapping chromosomes is difficult because, traditionally, tools could only read short segments of DNA at a time. Using “nanopore technology,” which funnels single molecules of DNA through a tiny hole and sequences them by detecting changes in the current flow, the team was able to get the first complete picture of an X chromosome sequence. 

The X chromosome is one of the sex-determining chromosomes passed down from parent to child in humans. The team filled in gaps in the sequence at the center and ends of X chromosomes, which are known as centromeres and telomeres respectively. This new information includes some 3.1 million base pairs of repetitive DNA. 

So what have they found from the newly mapped areas? The team has discovered that, in fact, some of the new regions they’ve sequenced hold rich information on variation within human populations. 

There are 23 other chromosomes left to be mapped and the team plans to finish the project by the end of 2020. This new information about human DNA could hold vital details about human genetics and biology, specifically surrounding disease. Knowing more about the most basic unit of our genetic makeup could provide a more complete picture of who we are as humans and how our species came to be.