The look deep into the swabs’ structures with the electron microscope showed that absorption, at least, was
determined more by the tip dimensions and the fiber arrangement—and less by the material itself.
Recovery is a challenge because of DNA interacting with the swab material itself, the researchers added.
“This is thought to be due to the chemical interaction of DNA molecules with the swab surface functional
groups,” they write.
By tradition, bone DNA work has forensically focused on tapping the innermost parts of the long bones—
the central part of the femur, for example.
But a team of scientists from Michigan State University are instead finding that there is a vast complexity
within a single bone’s DNA sources—and the ends may be a better bet for collecting DNA. The findings
were also published in June in the Journal of Forensic Sciences.
“Both nuclear and mitochondrial DNA quantities vary significantly depending on the femoral location
assayed, and can differ as much or more within a skeletal element,” the authors write. “The research present-
ed here demonstrates that, in the relatively fresh bone examined, nuclear and mitochondrial DNA quantities
vary significantly within a single skeletal element, and that within-bone variation can be greater than that
The scientists took the bones from pigs and cows, and measured the DNA before and after months of
exposure—either underground, or on the ground out in the elements of Michigan. The parts included femurs,
heel bones and ankle bones, according to the paper.
The bones were drilled, and the DNA was amplified through PCR on an iCycler thermal cycler made by
The greatest DNA amounts were gleaned from the epiphyses, or the ends of the bones, with less genetic
material from the metaphyses, and the muscle attachment sites.
Over time, of course, there was less DNA. But the rates of decline differed greatly.
In contrast to popular wisdom, the least DNA—both nuclear and mitochondrial—was found in the diaphysis, the central shaft. That finding could turn forensic DNA on its head, according to the paper.
“Overall, femoral epiphyses harbored more DNA than metaphyses, and both had more than the diaphysis,”
the paper concludes. “These data clearly have important implications for forensic (anthropologists and biologists) that utilize skeletal material for DNA analyses and identifications.”
Degraded DNA, forking family trees
The arrest of the alleged Golden State Killer in April, decades after a
run of rapes and murders up and down California, launched advanced genetic genealogy into the public consciousness. The technique—which had
produced a handful of cold case breakthroughs over the last two years—has
led to arrests in decades-old unsolved killings that had detectives stuck.
A handful of the cases have also shown a pioneering method of analyzing degraded DNA that went unrefrigerated or unpreserved for years, and
The DNA Doe Project has solved two of the cases with severely degraded DNA, finding a way to interpret the missing pieces and then run it
through public databases to positively identify a growing group of unidentified deceased persons.
“The key is work with degraded DNA,” said Colleen Fitzpatrick, a
genetic genealogist who founded the DDP with colleague Margaret Press.
“This is not just a breakthrough on genealogy at work. We have adapted the
existing tools, and we have developed new tools, and to apply the genealogy
The “Buck Skin Girl,” who went unidentified
for 37 years, was identified as Marcia L.
King through genetic genealogy.