solve. However, a better approach is to find a path that passes through each link of the network exactly once. (Note that it may visit some nodes repeatedly. These correspond to repeated strings in the genome.) This problem, called the Eulerian path problem, has a computationally efficient solution, which makes next-generation sequencing practical (especially for other animal species, which have no reference genome to consult).

The application of the mathematical sciences to the genome stands to have a great impact on society

The application of the mathematical sciences to the genome stands to have a great impact on society. A Battelle Memorial Institute study in 2011 concluded that the economic impact of the Human Genome Project has nearly reached $800 billion—quite a return on the U.S. government’s $3 billion investment. And that doesn’t even begin to account for the impact on humans, which is just beginning.

For example, in 2010 a 39-year-old patient was admitted to Barnes-Jewish Hospital in St. Louis with leukemia. There were two possible diagnoses with two different treatments. The patient had symptoms of a form of leukemia called APL, which responds well to chemotherapy. At the same time she had symptoms of another condition that would require a stem cell transplant, a risky procedure that can itself be fatal.

The standard genetic test for APL looks for two regions on chromosomes 15 and 17 that are swapped. That test came back negative. As an experiment, the patient’s doctors spent $40,000 and six weeks to sequence her genome, comparing her skin cells to her cancer cells. In the cancer cells, they found about 77,000 base pairs of her chromosome 15 had been inserted into the chromosome 17—too small a fragment for the standard test to detect but easily detectable by genomics. Since then, they have identified similar genetic alterations in two other leukemia patients.

The doctors went on to treat the patient with the anti-APL drug instead of the dangerous stem cell transplant. It eliminated her cancer cells, and she was still in remission 15 months later. This is exactly the sort of individualized medicine that doctors dreamed the Human Genome Project would make possible. Though such medicine is still experimental today, with continued progress in bioinformatics it will probably be common a generation from now.

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