Cold DNA

Cold DNA

   Our DNA (dioxyribonucleic acid) is a fascinating building block, and is something that we share with so many other organisms.  But despite all of that, each of our DNA spectrums is unique, something that emerged in a recent article in The Atlantic titled A Death at Torrey Pines by James Vlahos.  The cold case (basically, a police investigation that has remained unsolved and has been filed away for possible later re-investigation) involved a rather brutal set of murders on the beach near San Diego, murders several years apart and yet showing similar characteristics.  The first suspect, a transient, claimed to have seen one of the teenage victims and was getting messages from her since her death...he later committed suicide.  The second suspect, a convicted rapist, had his DNA found on one body but not on the other (he was in prison at the time), confounding the detectives who felt that the two murders were done by the same killer.  He (the second suspect) then died under mysterious circumstances near the ocean.  The third --and most recent-- suspect, was one of the police officers investigating the case.  His after-work life was questionable ("kinky" was one nickname given to him by his workers) and further investigation discovered his DNA (in this case, what was thought to be sperm) on the body.  He (the final suspect) also committed suicide.

   Rather than bring up a murder case, however, the interesting point here was the DNA processing.  An investigation looks for DNA evidence at a crime scene, even ones quite far in the past.  Every now and then you'll read a story about an incarcerated prisoner being released after years or decades in prison after DNA testing proved negative in that case.  So how is it done?  After all, here's how complicated our DNA can be (and is) according to the site National Human Genome Research Institute telling how DNA: ...contains the biological instructions that make each species unique.  DNA, along with the instructions it contains, is passed from adult organisms to their offspring during reproduction...In organisms called eukaryotes, DNA is found inside a special area of the cell called the nucleus.  Because the cell is very small, and because organisms have many DNA molecules per cell, each DNA molecule must be tightly packaged.  This packaged form of the DNA is called a chromosome. During DNA replication, DNA unwinds so it can be copied.  At other times in the cell cycle, DNA also unwinds so that its instructions can be used to make proteins and for other biological processes.  But during cell division, DNA is in its compact chromosome form to enable transfer to new cells... Researchers refer to DNA found in the cell's nucleus as nuclear DNA.  An organism's complete set of nuclear DNA is called its genome.  In this particular case (and others) says the article:...analysts check at least 13 key locations in the strands of DNA to create a numerical profile.  The profile is then entered into the FBI's Combined DNA Index System, or CODIS, to see whether it matches the profile of anyone already in the system.  In the best-case scenario, with genetic information from all 13 locations successfully identified, the chance of an incorrect, coincidental match is less than one in 200 trillion.

   The sequencing of one's DNA is now nearing the affordable point for the average person.  From over $10,000 some years ago to about $200 now (such a product is offered through National Georgraphic's Genographic Project).  Although first postulated back in 1869, and later refined in 1944, it wasn't until 1953 that the famous "double-helix" model was proposed by James Watson and Francis Crick.  Two years later, Fred Sanger's experiments with amino acids and insulin completed the sequencing puzzle we now take for granted.  In the case of the police file mentioned earlier, large scale sequencing was used, something "simply" explained this way in Wikipedia: Large-scale sequencing often aims at sequencing very long DNA pieces, such as whole chromosomes, although large-scale sequencing can also be used to generate very large numbers of short sequences, such as found in phage display.  For longer targets such as chromosomes, common approaches consist of cutting (with restriction enzymes) or shearing (with mechanical forces) large DNA fragments into shorter DNA fragments.  The fragmented DNA may then be cloned into a DNA vector and amplified in a bacterial host such as Escherichia coli.  Short DNA fragments purified from individual bacterial colonies are individually sequenced and assembled electronically into one long, contiguous sequence. Studies have shown that adding a size selection step to collect DNA fragments of uniform size can improve sequencing efficiency and accuracy of the genome assembly.  In these studies, automated sizing has proven to be more reproducible and precise than manual gel sizing.

   Phew...feel like you're back dozing off in school?  So where is all this talk about DNA headed?  As the original Torrey Pines' piece asked, could this all be too much for us to handle (in this case, is DNA so prevalent that "stray" DNA can contaminate a site): Problems do occur with DNA evidence, however—not because the underlying science is flawed, but because the people practicing it are.  Contamination can take place when DNA from one case taints evidence from another, or when a crime-lab employee’s own DNA gets into case materials.  Problems can occur when a criminalist sneezes, touches lab equipment, or even talks near an evidence sample.  Shaking hands can transfer DNA from one criminalist to another.  “With the sensitivity of these instruments, just a few cells are needed,” says Greg Hampikian, a professor of biology and criminal justice at Boise State University.

   A few cells?  Conservationist Carl Safina, author of Beyond Words...What Animals Think and Feel, wrote: Complex animals have inherited very ancient emotional systems.  The genes that direct our own bodies to create the mood-making brain hormones oxytocin and vasopressin, for instance, date back at least seven hundred million years..."The same neural mechanisms are at work in worms and humans," wrote S.W. Emmons in a 2012 article with the intriguing title, "The Mood of a Worm."  He's referring to the tiny one-millimeter-long C. elegans -- the elegant nematode.  Here's the thing: the worm has nearly the same suite of genes that underlie the nervous systems of humans, giving the worms "connectivity patterns also found in the human brain."  C. elegans has just 302 nerve cells (Humans have roughly 100 billion).  Yet C. elegans produces a motivating chemical similar to oxytocin, called nemotocin, and its function is familiar...Emmons, who is a professor at the Albert Einstein College of Medicine, leaves us with this insight:  "Just as today's major roads and highways may once have been ancient trails, biological systems can retain essential features derived from their origins...it is a mistake to consider small invertebrates as primitive.

   We share much with the animal world, not especially surprising since, as author Safina notes, we are animals.  But the sharing of DNA might be much more extensive than we imagined.  And indeed, this was somewhat the premise of the movie some years ago, Prometheus, where DNA survival was the main goal, ancient alien civilizations far superior to ours, still searching for the right "carrier" to continue its (DNA's) evolution (in this case, humans and other organisms on earth fit the bill).  With so much information in just a few cells (from saliva to hair), imagine what we have yet to discover.  Our ancient past might find us linked with far more than earthly creatures...but it's a good place to start.