Viruses in the Genome
Carl Zimmer has an excellent post on viruses in the human genome. Here is the juicy snip:
The human genome carries full-fledged retroviruses, as well as
viruses in various state of decay. Scientists have identified 98,000 of
these viruses, along with about 150,000 fragments of defunct viruses.
All told, they make up 8 percent of the human genome. In many cases,
the virus genes have disappeared altogether, leaving behind flanking
repeats, which have been duplicated to millions of copies that take up
about 40 percent of the genome. As a point of comparison, our "own"
genes–in other words, those that encode proteins that make up our
bodies and allow our bodies live–make up only about one percent of the
Some of these endogenous retroviruses are only found in some people
and not others. They must have invaded someone’s genome and then spread
to his or her descendants, but have not yet spread throug our entire
species. Others appear to be ubiquitous–meaning that they are ancient
passengers that had already spread throughout an ancestral population.
Read the whole piece.
Carl Zimmer, The Sixty-Million Year Virus. The Loom, March 13, 2006.
Norbert Bannert, and Reinhard Kurth. Retroelements and the human genome: new perspectives on an old relation. PNAS. October 5, 2004. vol. 101 (Suppl. 2) 14572-14579. [A nice open-access review article on human endogenous retroviruses (HERVS)]