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Dr. Adam Siepel, Cornell University – Similarity in Primate DNA

In today’s Academic Minute, Dr. Adam Siepel of Cornell University explains why humans and chimpanzees are drastically different despite sharing much of the same DNA.

Adam Siepel is an associate professor of biological statistics and computational biology at Cornell University where his research explores the intersection of statistics, computer science, evolutionary biology, and genomics. His current focus is the development of computational methods for the identification of functional elements in genomes. He earned his Ph.D. at the University of California Santa Cruz.

About Dr. Siepel

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Dr. Adam Siepel – Similarity in Primate DNA

By the early 1970s, scientists thought they had a pretty good idea of how evolution worked.  Some random mutations in DNA make organisms more fit and therefore tend to become more common over time.  These advantageous or adaptive mutations were thought to occur primarily in portions of the DNA that encode proteins, the essential molecules that do most of the work of living cells.  But when scientists started to actually measure the proteins in humans and chimpanzees, they found a surprise: these proteins were nearly identical!  What, then, could explain the pronounced differences in physiology and behavior between our ape cousins and ourselves?

Some biologists began toying with a radical idea, which was given full voice in a famous 1975 paper by Mary-Claire King and Allan Wilson.  What if humans and chimpanzees differed not so much because of their proteins as because of the regulatory sequences that turn those proteins on and off?

Only recently has it become possible to examine King and Wilson's proposal empirically, using massive data sets based on modern genomic technologies.  This is where our study comes in.  We devised a mathematical model of the processes of mutation and natural selection, and applied it to rich data sets describing regulatory sequences and genetic variation in primates. We found that, just as King and Wilson surmised nearly 40 years ago, human regulatory sequences do appear to have been strongly influenced by natural selection, and many show clear signs of evolutionary adaptation.  Indeed, regulatory sequences appear to have contributed at least as many advantageous mutations as protein-coding sequences.

Our analysis suggests that gene regulation is an essential part of what makes us human.  In other words, when it comes to genes and evolution, "it's not [just] what you got, it's how you use it".

Production support for the Academic Minute comes from Newman’s Own, giving all profits to charity and pursuing the common good for over 30 years, and from Mount Holyoke College.

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