Scientists find a fingerprint of evolution across the hu...( The Human Genome Project revealed th...)

The Human Genome Project revealed that only a small fraction of the 3 billion letter DNA code actually instructs cells to manufacture proteins, the workhorses of most life processes. This has raised the question of what the remaining part of the human genome does. How much of the rest performs other biological functions, and how much is merely residue of prior genetic events"

Scientists from Cold Spring Harbor Laboratory (CSHL) and the University of Chicago now report that one of the steps in turning genetic information into proteins leaves genetic fingerprints, even on regions of the DNA that are not involved in coding for the final protein. They estimate that such fingerprints affect at least a third of the genome, suggesting that while most DNA does not code for proteins, much of it is nonetheless biologically important important enough, that is, to persist during evolution.

To gauge how critical a particular stretch of DNA is, biologists often look at the detailed sequence of letters it consists of, and compare it with a corresponding stretch in related creatures like mice. If the stretch serves no purpose, the thinking goes, the two sequences will differ because of numerous mutations since the two species last shared an ancestor. In contrast, its believed that the sequences of important genes will be similar, or conserved, in different species, because animals with mutations in these genes did not survive. Biologists therefore regard conserved sequences as a sign of biological importance.

To test for conservation, researchers need to find matching stretches in the two species. This is relatively easy for stretches that code for proteins, where scientists long ago learned the meaning of the sequence. For noncoding regions, however, the comparison is often ambiguous. Even within a gene, stretches of DNA that code for pieces of the target protein are usually interspersed with much
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