May 15, 2007
Large DNA Structural Variations Target Of Study

Single DNA letter differences have garnered most of the popular and scientific attention for the study of human genetic differences. But larger genetic differences such as large copy variations (where people differ in how many copies they have of genes and sections of genes) have come under greater scrutiny as researchers have developed techniques to measure these differences. Studies of large DNA structural variations have begun to bear fruit.

A major new effort to uncover the medium- and large-scale genetic differences between humans may soon reveal DNA sequences that contribute to a wide range of diseases, according to a paper by Howard Hughes Medical Institute investigator Evan Eichler and 17 colleagues published in the May 10, 2007, Nature. The undertaking will help researchers identify structural variations in DNA sequences, which Eichler says amount to as much as five to ten percent of the human genome.

Past studies of human genetic differences usually have focused on the individual “letters” or bases of a DNA sequence. But the genetic differences between humans amount to more than simple spelling errors. “Structural changes — insertions, duplications, deletions, and inversions of DNA — are extremely common in the human population,” says Eichler. “In fact, more bases are involved in structural changes in the genome than are involved in single-base-pair changes.”

Efforts to estimate the amount of genetic difference between people and groups have produced underestimates of the real differences. The newer studies of genetic differences which measure large copy variations (e.g. differences in the number of copies of genes or sections of genes) are finding much larger differences between humans. I suspect these differences show how much local selective pressure humans experiences in each local environmental niche they moved into. We are not as alike as the politically correct would have us believe.

Eichler and colleagues are searching for large copy variations in DNA taken from 62 people.

Using DNA from 62 people who were studied as part of the International HapMap Project, they are creating bacterial “libraries” of DNA segments for each person. The ends of the segments are then sequenced to uncover evidence of structural variation. Whenever such evidence is found, the entire DNA segment is sequenced to catalog all of the genetic differences between the segment and the reference sequence.

The result, says Eichler, will be a tool that geneticists can use to associate structural variation with particular diseases. “It might be that if I have an extra copy of gene A, my threshold for disease X may be higher or lower.” Geneticists will then be able to test, or genotype, large numbers of individuals who have a particular disease to look for structural variants that they have in common. If a given variant is contributing to a disease, it will occur at a higher frequency in people with the disease.

Their use of DNA from people studied in the International HapMap Project creates synergies between the databases generatd by each effort. The International HapMap Project involves measuring single letter differences. Some of the single letter differences correlated with variations in structures such as deletion mutations and in number of copies of each gene.

We live in the twilight of the era of when little has been known about how genetic variations create human variations in health, appearances, intelligence, personality and other human qualities. 20 years from now we are going to know in enormous detail which genetic variations matter and how they matter. Continued declines in the cost of DNA testing will provide scientists with orders of magnitude more genetic data than they have now.

Once we know what most of the genetic variations mean I expect many changes in how we live our lives. For example, I expect those involved in romantic courtships to either surreptitiously get DNA samples from potential mates or demand DNA testing info as a prelude to serious courting.

Share |      Randall Parker, 2007 May 15 09:38 PM  Biotech Advance Rates


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