CASE 3 YOU, FROM A TO T: YOUR PERSONAL GENOME

The goal of the Human Genome Project, which began in 1990, was to sequence the human genome as well as the genomes of certain key organisms used as models in genetic research. The model organisms chosen are the mainstays of laboratory biology—a species each of bacteria, yeast, nematode worm, fruit fly, and mouse. By 2003, the genome sequences of these model organisms had been completed, as well as that of the human genome. By then, the cost of sequencing had become so low and the sequence output so high that many more genomes were sequenced than originally planned. Genome sequencing is even cheaper today, and soon you can choose to have your personal genome sequenced.

Why sequence more genomes? And if the human genome is sequenced, why sequence yours? As we saw in Case 3: You, from A to T, there is really no such thing as the human genome, any more than there is the fruit fly genome or the mouse genome. With the exception of identical twins, every person’s genome is unique, the product of a fusion of a unique egg with a unique sperm. The sequence that is called “the human genome” is actually a composite of sequences from different individuals. This sequence is nevertheless useful because most of us share the same genes and regulatory regions, organized the same way on chromosomes. Detailed knowledge of your own personal genome can be valuable. Our individual DNA sequences differ at millions of nucleotide sites from one person to the next. Some of these differences account in part for the physical differences we see among us; others have the potential to predict susceptibility to disease and response to medication. For Claudia Gilmore, knowledge of the sequence of her BRCA1 gene had a significant impact on her life.

Determining these differences is a step toward personalized medicine, in which an individual’s genome sequence, by revealing his or her disease susceptibilities and drug sensitivities, allows treatments to be tailored to that individual. There may come a time, perhaps within your lifetime, when personal genome sequencing becomes part of routine medical testing. Information about a patient’s genome will bring benefits but also raises ethical concerns and poses risks to confidentiality and insurability.