"
Junk" DNA includes a whole subset of names such as introns, retrotransposable elements, and non-coding RNAs (ncRNAs).[...]
The greatest shock of genomic science was to find that
the human genome contains more viral than "human" genes.[...]
Most genetic diversity can be found in virus genes. Scientists agree that there are some 1,000,000,000,000,000,000,000,000,000,000 viruses in the ocean, and genetically they match almost nothing compared with genes from any microbe, animal, plant or other organism, even from any other known virus.
All living things have hundreds or thousands of genes imported by viruses. There is a group of viral species known as retroviruses which insert their genetic material into the host cell's DNA. When the host cell divides, it copies the virus's DNA along with its own. Retroviruses have "on switches" that prompt their host cell to make proteins out of nearby genes.
Sometimes their switches turn on host genes that ought to be kept shut off, and cancer can result.
This is precisely what our junk DNA - ncRNA- seems to be doing "next" to genes that have to do with stem cells and cancer cells.
What is known as
endogenous retrovirus - endogenous meaning generated within - are the viruses that lurk in the genomes of just about every major group of vertebrates, from fish to reptiles to mammals. Virologists have found retrovirus-like segments in our human genome and they were able to track its genetic code down to an original functioning virus. The virus was called Phoenix, for the mythical bird that rose from its own ashes.
It is known that part of our junk DNA,
the retrotransposable elements, is viral in its origin.
It includes the endogenous retroviruses. But
it is now argued that ncRNA (non coding RNA) might be viral in its origin as well.[3] This has interesting implications in the sense that epigenetic control of gene expression involves this junk DNA - ncRNAs.[4] It would mean that
our entire junk DNA (98%) might well be very functional epigenetically speaking (more info on epigenetics below), and active in the induction of regulatory genes [...]
As it happens, a paper came to my attention just recently. I think it is very relevant in the sense that the fragments of hemorrhagic viruses that were speculated to be the cause of the Black Death (for more information see
New Light on the Black Death: The Viral and Cosmic Connection), are listed as part of our genome, indicating that life on Earth has been exposed to rather dangerous viruses through our evolutionary history which then effected changes in our DNA: