Deciphering Human Differences
Chunks of shuffled DNA in the human genome could underlie many diseases
Source: “Paired-End Mapping Reveals Extensive Structural Variation in the Human Genome”
Michael Egholm, Michael Snyder, et al.
Science 318: 420-426
Results: Scientists have uncovered extensive regions in the human genome where chunks of DNA have been deleted, copied, or completely rearranged. More than a thousand structural variations were identified between two individual genomes–many more than other studies have found.
Why it matters: Most studies of genomic variation have focused on individual bases, or DNA “letters.” In the last few years, however, several studies have shown that structural variations in DNA may be at least as important as single-letter variations. Mapping and characterizing these structural variants could be key to understanding human diversity and the origins of many diseases.
Methods: Snyder and his colleagues analyzed the genomes of two individuals, one of African descent and one of European descent. They chopped the genomes into millions of fragments, each 3,000 bases long, and tagged the fragments’ ends. They then sequenced the ends of each fragment and compared them with a reference genome, derived from the Human Genome Project. If the overall sequence of the fragments was either shorter or longer than the corresponding piece of the reference genome, the researchers concluded that a piece of DNA had probably been copied or deleted.
Next steps: The company whose sequencing technology was used in the study, 454 Life Sciences of Branford, CT, aims to repeat the experiment on 100 individuals. Scientists eventually aim to generate an inventory of the structural variations associated with human disease.