A: “With the exception of genetically identical twins, each person’s genome is a unique combination of DNA sequences that play major roles in determining who we are. Intense research is ongoing to understand genetic differences between people. Why the interest from science? By understanding how one person’s DNA differs from another’s, we may uncover variations that not only create our individual traits, such as how we look, but also create susceptibilities to a myriad of diseases.

“Repetitive DNA sequences have long been understudied but are important to what makes each of us genetically unique. Scientists used to call these repeating sequences ‘junk DNA,’ and their importance has remained undiscovered because technical barriers made them hard to identify and study. Recently, research groups at Johns Hopkins have overcome those challenges to develop methods to map these repeating sequences. We’ve found that they play a key role in determining the uniqueness of our genome. Our research confirms that repetitive DNA sequences don’t stay in the same place—they move around in the human genome and insert copies of themselves here and there. They can also mobilize—‘copy and paste’—other sequences. Together, these insertions actually make up a large fraction of our DNA, and we think that understanding them will be important in giving us clues as to an individual’s unique risk of contracting disease.”

—Kathleen Burns, an assistant professor of pathology at the School of Medicine, is the leader of one of three Hopkins labs attempting to unravel the sometimes-unpredictable nature of DNA.