From an article Justin Zooby and published in the National Institute of Standards and Technology (NIST) (an agency of the United States Department of Commerce) web site:  

Twenty years ago, scientists mapped more than 90% of the entire human genome. A huge accomplishment involving many scientists, mapping our genes has allowed researchers to better understand inherited diseases and led to many other scientific advancements.  

If a researcher wanted to analyze your DNA, they’d compare you to that single reference genome that’s been in use for years and try to figure out how your DNA is different from that reference.

Last year, we were part of a large international team that finished the last 8% and completed the first human genome. This has enabled insights into previously unexplored parts of the genome, including providing a map of millions of genetic variations, or stretches of DNA that vary from person to person.

But here’s the problem — the composite human genome, while taken from a diverse group of people from all over the world, does not represent the full diversity of human DNA. Even the first “complete” human genome is missing sequences that only exist in some individuals. That can make medical research or testing someone’s genes for diseases a challenge for scientists. This is especially true for people with ancestry from regions of the world that have high genetic diversity — though it affects everyone. 

Say you have an extra copy of a gene that’s not in the reference. That could be missed when comparing your DNA to the standard reference.   

My colleagues and I are helping scientists make a new form of a genome — the pangenome — or “all genome.” The pangenome has been released in a draft version with about 50 people’s DNA, with the long-term goal of having about 350 people’s DNA in the completed pangenome in the next two or three years. It will allow us to understand the full diversity of our genes and advance medical research. 

So instead of researchers comparing one person’s DNA to one standard reference, researchers can compare the person’s DNA to a reference library containing potentially hundreds of diverse people’s DNA. 

You can read the full article at: https://tinyurl.com/b96njehx.