What's in your genes?

You may not know it, but you're part virus. At least, some of your genes come from viruses that slipped their DNA into the genes of our primate ancestors millions of years ago. The DNA remnants of these ancient "retroviruses," distant relatives of today's HIV, account for an estimated 8 percent of the human genetic code and may have enabled master genes that account for some of the differences between us and our chimpanzee relatives. Master genes: Not all genes are created equal; the master genes can turn the others on and off, thus gaining control over genes related to cell division, DNA repair and programmed cell death. (This regulation of genes allows for tighter control of gene expression (i.e. which genes are turned on or off), which can account for the wide differences between humans and other apes, despite our very similar genetic codes. One such gene, called p53, has the job of coordinating the surveillance system that monitors the well-being of cells. It is so important in this job that when it fails, cancer is often the result—biologists even call it the "guardian of the genome.

" Scientists had long wondered how genes such as p53 built their powerful empire over other genes. A new study detailed this week in the online edition of the journal Proceedings of the National Academy of Sciences implicates the ancient retroviruses as the force behind p53's rise to power.