In the century and more since Charles Darwin first advanced his theory of evolution, the proposal has come to dominate biological understanding. Current thinking has it that new traits arise spontaneously through genetic mutations, and, if they promote the survival of the individual, the genes may be selected for in subsequent generations. Over time, significant changes in a species can occur in this way -- indeed, entirely new species may eventually appear.
In this age of molecular biology, highly specific new questions about the process of evolution are being framed. Scientists would like to know whether and how evolution operates at the molecular level in an organism's DNA.
Now, experiments performed at the University of Pennsylvania Medical Center have revealed a molecular mechanism that may be a significant driver of evolution in humans and other mammals. Certain retrotransposons -- bits of DNA able to copy themselves from one region of the genome to another -- are able to pick up flanking genetic sequences and then insert themselves and the tag-along DNA at new locations. A report on the new study will appear in the March 5, 1999, issue of Science. (Advance copies of the paper are available to reporters through the journal's news office at 202-326-6421.)
"These findings suggest a new mechanism for shuffling important genetic sequences -- exons, promoters, enhancers -- that may lie downstream from these active mobile DNA elements," says Haig H. Kazazian, MD, chairman of the department of genetics and senior author on the paper. "From an evolutionary perspective, here is a way to create novel genetic combinations. While many such changes might prove lethal, some could improve function in individuals, leading to a selective advantage for those individuals."
"Previously proposed explanations for how such rearrangements of DNA
might occur have been rather murky," says lead author John V. Moran, PhD, now an
Contact: Franklin Hoke
University of Pennsylvania School of Medicine