Whose Genome is It, Anyway?

A quick glance around any public gathering will attest to the physical diversity of the human population. In most groups of people, some will be tall, others hefty; some will have brown eyes, and others blue. Physical attributes such as height, complexion, and hair and eye color are largely determined by genes - packets of the genetic material DNA, which makes up chromosomes in the human cell.

As scientists begin to map and analyze the molecular details of the complete set of human genes, whose will it be? In many ways, describing the anatomy of the human genome will be similar to studying the human heart, for example, or the human brain. While there are small differences from person to person in the size and shape of these organs, most of the key characteristics are the same. Although human beings are distinct from one another, they are really very similar in most biologically important respects. That's what makes us human. So the map of the human genome can really be based on information collected from many different people. And most of the information in that map will pertain to everyone.

The tiny differences between any two people rest in only 2 to 10 million (out of the 3 billion total) nucleotide bases, an amount that computes to about 1 percent or less of their total DNA. Because these small differences vary from person to person, it doesn't matter whose genome it is. For some studies, the differences will be the focus of interest. In other cases, it will be the similarities. Researchers at Baylor College of Medicine were given the assignment of mapping the sex chromosome X and chromosome 17. They collected DNA from patients who came into the clinic for genetic testing. Each sample is from a different and unrelated person. The cell culture collection contains a number of different human genomes.

Eventually, scientists will "map", or establish distinctive genetic landmarks, from one end of a chromosome to the other and add that information to the genetic map of the entire human genome. This complete map will become the "reference" to which researchers will compare DNA taken from a variety of people, as scientists look for disease genes and other important genetic regions located on chromosomes. A particular region on a chromosome, for example, may be found to contain information about height. Although the genetic content of that specific site may change slightly from person to person, the location of the site will be the same in each person's genome.

Because studying the entire six-foot stretch of human DNA is a huge project, scientists are tackling the genome one chromosome at a time. Even then, analyzing the information in just one chromosome is an enormous task for a single research group, so many scientists are studying only portions of a chromosome at a time. Even then, analyzing the information in just one chromosome is an enormous task for a single research group, so many scientists are studying only portions of a chromosome. The complete map for a single chromosome will then be derived from samples collected from several unrelated people by researchers in many different laboratories.

For several decades, geneticists searching for disease genes have studied human cells maintained in the laboratory. These cells originally came from people who have an inherited disease, from their healthy relatives who are carriers, or from other unrelated healthy people. But because human cells do not ordinarily survive long under laboratory conditions, scientists have had to invent ways to keep the cells alive long enough to perform detailed studies of DNA inside the cells.

Since almost all cells in the body contain the same genetic information, nearly any type of cell can be used as a source of DNA. A type of white blood cell called a lymphocyte is commonly used because it is easy to obtain from a blood sample. To get the cells to last longer in the laboratory, scientists infect lymphocytes in the test tube with a common virus known as EBV. This virus, the cause of mononucleosis, interrupts the cell's normal life cycle so it literally doesn't know when to die. Cells "immortalized" by EBV then grow and divide indefinitely in laboratory cultures, providing researchers with unlimited amounts of human DNA for genome studies.

In most labs, the donors of these pieces of biology's greatest puzzle will never be known. They are the genetic equivalent, according to one researcher, of the unknown soldier.

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