By Jonny Lupsha, Wondrium Staff Writer
According to a new report published in Nature Communications, scientists have extracted a complete human genome from a 5,700-year-old sample. They took it from a chewed pitch of birch, which is believed to have been used for adhesive and personal health purposes. The human genome is the biggest genetic picture of us.
With the newly discovered piece of birch in southern Denmark, scientists have developed a tremendous snapshot of Europe nearly six millennia ago. “It does not only contain ancient human DNA, but also microbial DNA that reflects the oral microbiome of the person who chewed the pitch, as well as plant and animal DNA which may have derived from a recent meal,” the report said.
“The individual who chewed the pitch was female and genetically more closely related to western hunter-gatherers from mainland Europe than hunter-gatherers from central Scandinavia. We also find that she likely had dark skin, dark brown hair, and blue eyes.”
The report even went so far as to state that the researchers found DNA fragments from several families of germs, including the Epstein-Barr virus, indicating that the disease afflicted the young woman. So what is the human genome and how was it possible to learn so much from what was essentially 5,700-year-old chewing gum?
The Human Genome Project
The human genome consists of “all the DNA, all 23 chromosome pairs of a human, and all the nucleotides,” said Dr. David Sadava, Adjunct Professor of Cancer Cell Biology at the City of Hope Medical Center. So what would be the challenge in genetically mapping all those?
“Chromosomes are extremely long—a typical human chromosome, on the average, is 100 million base pairs of DNA,” Dr. Sadava said. And the computers that can map them? “These machines can sequence 800 base pairs at a time. So what are we going to do? We’ll cut the 100 million base pairs into 800-base-pair fragments.”
In addition to the minute size of each DNA fragment compared to an entire chromosome, the computers that map them could only do so in random order. Therefore, in order to complete the chain, scientists had to look for specific sets of DNA base pairs, called landmarks, which they knew belonged in certain places along the chromosome and then put the pieces of the puzzle into place around them.
It was comparable to having a 10,000-page book spread out before you in neatly torn-out and unnumbered pages, then knowing that a certain phrase only appeared on page 42 of the book and finding that phrase. Once you find that page and you know it’s page 42, you build outwards from there based on the first and last lines of page 42.
Dr. Sadava said it took scientists 10 years just to know where each of those specific sets of base pairs—or phrases of the book, in this example—went, then several more years to arrange them.
“The other way of doing it is called shotgun sequencing,” Dr. Sadava said. “What they did was the same thing using landmarks, only they had a computer find them. What they did was take the chromosome, bust it into 800-base-pair fragments, feed the sequences into a computer, and have the computer line it up for you.”
Dr. Sadava said this created a whole new field called bioinformatics, and it only took a year to do, despite the incredibly advanced computer work that was involved.
Now that the human genome has been fully mapped, we can get far better and more detailed information about the ancient world. Questions about early humans that have gone unanswered for centuries may soon be answered.
Dr. David Sadava contributed to this article. Dr. Sadava is Adjunct Professor of Cancer Cell Biology at the City of Hope Medical Center. Professor Sadava graduated from Carleton University as the science medalist with a B.S. with first-class honors in biology and chemistry. A Woodrow Wilson Fellow, he earned a Ph.D. in Biology from the University of California, San Diego.