My Brother, The Bloodsucker
This little fellow is a Rhodinus prolixus, aka South American bloodsucker, and his DNA may be in my DNA! Don't be smug now... It could be in yours too. And though maybe he's not our brother, he might very well be a distant cousin. So don't step on him.
When we think about DNA, we think about the genes contributed by our parents, grandparents, and so forth, in a direction that goes vertically back through our ancestry. As recently as 2008, however, genome biologist Cédric Feschotte and his team at the University of Texas at Arlington, discovered the first unequivocal evidence of horizontal DNA transfer.
Froschette and his colleagues used computer programs to compare the distribution of mobile genetic elements among 102 animals whose genome sequences are available. Paul J. Brindley of George Washington University Medical Center in Washington, D.C., contributed tissues and DNA used to experimentally confirm the computational predictions of Feschotte's team.
This information led to Feschotte's current discovery - the first evidence that DNA can be transferred horizontally from non-mating species to mammals - - that millions of years ago transposons from parasites jumped sideways into mammalian species, integrating into the germ cells and ensuring their passage from generation to generation. Transposons are sequences of DNA that can jump around the genome of a single cell causing changes in the cell, sometimes positive, sometimes not.
The two species discovered to share DNA with their mammal hosts were the parasitic invertebrates Rhondinus prolixus, or South American bloodsucker, and the Lymnaea stagnalis, a pond snail. While the South American bloodsucker feeds directly on mammals (including humans), the pond snail feeds on parasitic worms that, in turn, feed on mammals.
Evidence that parasitic DNA was shared with mammals was found in the transposons of opossum and squirrel monkeys. This evidence fills a gap in our knowledge about human DNA, because when the human genome was sequenced ten years ago, it was found that nearly half of our DNA is derived from transposons.
Now the big question is how will these little buggers influence our evolution? To witness that, we might have to stick around for a few thousand, maybe millions of years. In the meantime, think of it this way... those transposons of the South American bloodsucker might actually be protecting our cells from certain bacteria and/or viruses.
In the future, if someone calls you a bloodsucker, you can smile, accepting the fact. Say, 'Yes, and I came by it naturally."
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