Scientists at Johns Hopkins University School of Medicine have found the reason behind our uniqueness - the physical characteristics and risks of disease.
Building on a tool that they developed in yeast four years ago, the researchers at scanned the human genome and discovered and identified a near complete catalog of the DNA segments that copy themselves, move around in, and insert themselves here and there in our genome.
The insertion locations of these moveable segments - transposons - in each individual's genome helps determine why some are short or tall, blond or brunette, and more likely or less likely to have cancer or heart disease.
Using their specialized "chip" with DNA spots that contain all of the DNA sequences that appear in the genome, researchers applied human DNA from 15 unrelated people.
The research team compared transposon sites first identified in the original published human "index" genome and found approximately 100 new transposon sites in each person screened.
"We were surprised by how many novel insertions we were able to find. A single microarray experiment was able to reveal such a large number of new insertions that no one had ever reported before. The discovery taught us that these transposons are much more active than we had guessed," said Dr. Jef Boeke, an author on the article.
Each of the 15 different DNA samples used in the study was purified from blood cells before it was applied to a DNA chip.
Transposons stick to spots on the DNA chip corresponding to where they're normally found in the genome, letting the researchers locate new ones.
Boeke's group first invented the transposon chip in 2006 for use in yeast.
But, it was Dr. Kathleen Burns, now an assistant professor of pathology at Johns Hopkins, who first got the chip to work with human DNA.
"The human genome is much larger and more complex, and there are lots of look-a-like DNAs that are not actively moving but are similar to the transposons that we were interested in," said Burns.
The trick was to modify how they copied the DNA before it was applied over the chip.
The team could copy DNA from the transposons of interest, which have just three different genetic code letters than other look-alike DNA segments.
"We've known that genomes aren't static places, but we didn't know how many transposons there are in each one of us; we didn't know how often a child is born with a new one that isn't found in either parent and we didn't know if these DNAs were moving around in diseases like cancer. Now we have a tool for answering these questions. This adds a whole dimension to how we look at our DNA," said Burns.
The study has been published in the latest issue of Cell.