Double-helix double up

Without any molecules to guide them, double helices of DNA with identical sequences can recognize one another from a distance and can even gather together. The DNA base pairs are complementary like right- and left-handed gloves, adenine bases with thymine, cytosine with guanine. Scientists at Imperial College London and the U.S. National Institute of Child Health and Human Development found that double-stranded DNA with the same sequences were about twice as likely to come together as DNA with different sequences, from a distance of up to three nanometers.