The genome of an ancient Greenlandic man was recently decoded by a large team of researchers led by Morten Rasmussen and Eske Willerslev at the University of Copenhagen using a tuft of hair so thick, it was thought to be from a bear.
His is now only the ninth of human genomes that have been fully decoded, joining a list of a Yoruba African, a Han Chinese, two Koreans and four Europeans. These genomes were decoded using relatively new advances in DNA sequencing technologies.
The hair sample, preserved in 4,000 year old permafrost, is from a male individual of the Saddaq culture, the first known people to settle in Greenland. This DNA strand is unique among its other decoded counterparts in that it survived relatively undamaged with contamination no higher than 0.8 percent, despite the fact that this is the oldest of the decoded DNA samples.
A major concern in ancient DNA studies is post-mortem damage, usually involving degradation of cytosine and uracil, two of the constituent nucleic acids that form the basis for DNA structure. This degradation can lead to confusion in interpreting the DNA code. Sometimes absences in the code cannot be definitively attributed to evolution of the species or simple loss of the gene after death.
The team painstakingly assessed and reassessed the DNA sample for contamination from newer DNA, but surprisingly found very little. This was mainly attributed to the preservation of the hair strands in permafrost.
In fact, the team was able to reconstruct the man's probable appearance and susceptibility to diseases from the near perfect DNA.
The presence of the Saddaq hair in Greenland is now substantial proof of the long-held theory that man first immigrated to the Americas over the Bering Strait from Siberia to Alaska, since the genome shows a close relationship to the early Chukchis of Siberia.
The advanced DNA sequencing technology used by the team was developed by Illumina, a biotechnology firm specializing in genetic variation and biological function based in San Diego. Using the Illumina system, they reported in the February 11 issue of Nature that they were able to decode approximately 80 percent of the genome to a high degree of accuracy.
To decode the meaning of the Greenlander's DNA, the team utilized a properties of DNA called single-nucleotide polymorphism (SNP) which involves a DNA sequence variation in just one nucleotide in order to distinguish the meaning of the gene. For example, if a gene's nucleotide is AAGCTC rather than AGGCTC, the mere knowledge of these single variations can lead to understanding of how humans develop diseases and respond to different stimuli like pathogens, chemicals, drugs and vaccines.
The DNA strand was also intended to be used to determine the origin of the Saddaq culture as well as its relationship with other early peoples of Asia and the Americas as well as present day populations.
"Competing theories have attributed the origins [of the Saddaq] to offshoots of the populations that gave rise to Native American populations such as the Na-Dene of North America, alternatively from the same source as the Inuit currently inhabiting the New World Arctic," said the team in the Nature article.
Unfortunately the specifics of the Saddaq origin are still not understood. A recent study involving the use of SNP technology established a comprehensive global coverage of the variations of the human genome among different populations. However, it was limited in its understanding of the variations and origins in Arctic populations.
The discovery of this large tuft of hair remains significant despite the setbacks in trying to further analyze it. It's remarkable completeness and lack of damage is rare in a sample so old. The next step is to look for a sample just as uncompromised but outside the Arctic region and not protected by permafrost.
