As new genetic testing becomes available on a regular basis, it may seem like we have it all figured out. But the truth is, there is still a whole lot that we don’t know about our genes.

The Human Genome Project (HGP) was completed in 2003 with successful mapping of all three billion molecules that form our DNA. The media exploded with headlines about the future of disease and promises of gene therapy, and the scientific community believed all of the answers to be at our fingertips. But we humans are not so simple.

Our DNA sequence is just one part of a multi-layered compilation of information. Think of the human genome like the Great American Novel. You can read the whole book, front to back, and get the gist of the plot. Then you can go back and try to find all of the author’s themes, metaphors, allegories, and all of the other literary devices that the author so cleverly embedded in every page. You might re-read the novel several times and keep finding new symbolism that didn’t manifest itself on your first read. Now imagine looking for each and every one of these subtle nuances in a multi-volume series. Now imagine looking through the entire New York Public Library.

While some genetic diseases are straightforward (having one or two malfunctioning copies of a particular gene will cause someone to have a disease), others are less so. Common diseases, such as diabetes, heart disease, and most cancers, are considered multifactorial; that is, they are believed to be caused by a combination of multiple genetic and environmental factors. Complex conditions, like schizophrenia, multiple sclerosis, and autism, appear to have a significant genetic component but there are no known genes that can undoubtedly predict whether someone will develop or be protected against the disease. Some genes are thought to be modifier genes, meaning that they may not be responsible for causing disease, but may modify its onset, course, or response to treatment. Others may be influenced by epigenetics, environmental or inherited changes that affect the way a gene is turned on and off in different cells and tissues of the body.

The HGP also found that the vast majority of our DNA does not encode actual genes, and was subsequently dismissed as “junk”. It doesn’t code for anything, so it can’t be important – right? Wrong! Long stretches of this this “junk” DNA have been preserved as intact for hundreds of millions of years, indicating an important purpose. But what is that purpose? The theory is that non-coding DNA provides some form of regulation of our genes. It may protect against gene destruction or control gene expression. But the fact remains that the double helix is holding onto many secrets that have yet to be revealed.

While it was not the end of the road, the HGP has permitted the identification of countless new diseases, the development of promising new therapies, and was a critical step in the right direction. And while we still have a ways to go before we have it all figured out, slowly but surely, the unknown is becoming the known.