Genetic Bar Codes

The quick, cheap way to identify—and diagnose—people using their genomes.

By Eva Gladek|Tuesday, November 14, 2006

There may be no invention more important to the smooth functioning of consumer commerce than the bar code, that pattern of skinny lines that turns a simple cash register into an impressive data-gathering device. Now, University of Wisconsin genome researcher David Schwartz hopes that DNA bar codes will be a similar shortcut for getting information about our health.

"You can take DNA molecules," says Schwartz, "and you can put a bar code onto these molecules very much the same way you can put a bar code onto frozen pizza."

As reported in Proceedings of the National Academy of Sciences, Schwartz's system for putting bar codes on DNA is a little more complicated than just printing a series of lines onto a cardboard box. But in important ways, it's simpler than conventional DNA sequencing, which was the method used in the Human Genome Project.

To use an analogy, if our genome is a long book, sequencing that book would involve carefully reading and transcribing every letter of the 3 billion base pairs that make up our genetic code. Rather than coming up with an individually sequenced genome for everyone, Schwartz's system looks at a sentence every few pages and also measures the distance between these landmark sentences. The idiosyncracies of each copy of the book are compared against a reference copy in our library—the fully sequenced human genome. This creates a customized genome-wide scan, revealing the areas of the genome that vary between individuals.

To do this with actual genes, Schwartz's team begins by sticking all six feet of the DNA molecules extracted from a cell onto a glass surface and allowing the DNA strands to elongate. The DNA is immobilized in this position and then exposed to restriction enzymes—biochemical scissors that cut DNA at very specific, recognized sequences of base pairs. Every place that the DNA is cut causes a gap to form. The result is a strand of DNA that has been dotted with a bar code-like pattern of gaps, which can be photographed and analyzed by powerful computers running specially designed software. Comparing these patterns against the sequenced genome gives a snapshot of the differences hidden in our personal genetic blueprints.

He says that using these bar code-like scans correctly could help doctors pick the best treatments for their patients, or even identify people at high risk for certain diseases. Schwartz says that even though this method doesn't provide every single letter of an individual's genome, it provides enough information to personalize certain medical treatments—like deciding for or against chemotherapy based on individual genetic odds of success. "There are trivial differences in terms of hair color, eye color, skin color," explains Schwartz, "but sometimes DNA is altered so that it can give rise to disease. The idea is to drive the cost down so that this becomes a tool that every doctor can have a chance to use," he says.

He estimates that they'll be commercially available within five years, with a fairly affordable price tag—well below a thousand dollars each. Not bad when compared to the $2.7 billion the Human Genome Project is estimated to have cost.

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