Ancient human genome studied
by R. Prasad
The ancient man, found in Greenland, had many physical
characteristics typical of those from northeast Asia For the first time
ever the genome of an ancient human has been studied. The 4,000-year-old
sample studied was a human hair of an Eskimo recovered from permafrost
sediments in Qeqertasussuk, Greenland. Four hair tufts were recovered
and only one was studied (sequenced).
The hair was from a Saqqaq man. Very little information is available
about Saqqaq culture as their remains are hard to find. The results were
published on February 11 in Nature.
Samples need to be well preserved and free of any contamination by
foreign DNA if a detailed genomic study is to be done. The Eskimo sample
met the criteria.
Well preserved The sample obtained has been excellently preserved.
This is because it was preserved in permafrost sediments. And this
allowed the scientists to study the sample in great detail.
The sample was relatively free of contamination with DNA of the
scientists or others who handled them. About 80 per cent of the DNA
recovered was that of the ancient Eskimo.
Apart from studying 79 per cent of diploid genome, the scientists
studied the mitochondrial DNA (mtDNA) and Y-chromosome DNA.
Mitochondrial DNA remains unchanged through generations and provides
information of the maternal lineage. The Y-chromosome reveals the
details of paternal lineage.
Northeast Asian origin based on the data generated, scientists were
able to describe many characteristics of the Saqqaq individual. The
characteristics are typical of northeast Asian origin.
For instance, he had black thick hair, skin colour that was more
Asian, eyes were brown, and teeth were typical of Asians. Metabolism and
body mass index clearly showed that the Saqqaq individual was adapted to
living in cold regions.
It became possible to describe the physical characteristics as the
genome had undergone specific point mutations (single-nucleotide
polymorphisms - SNP) in the coding region of the human genome.
Though all humans share about 99.9 per cent of the genome, specific
SNPs make Asians look different from Caucasians or play a role in
diseases by affecting the gene's function. SNPs can also help predict
the risk of developing particular diseases.
Based on the physical characteristics, scientists have been able to
deduce the migration of Saqqaq from East Siberia across the Bering
Strait.
Across Bering Strait "A single individual may, or may not, be
representative of the extinct culture that inhabited Greenland some
4,000 years ago," notes the paper. Yet, they go on to conclude that this
individual or a group did indeed cross the Bering Strait, and they did
it "independently of the ancestors of present-day Native Americans and
Inuit." But they are unequivocal about the northeast Asian
characteristics (phenotype) of the individual.
Geneticists have been particularly interested in studying samples of
ancient humans to understand the dispersal of humans out of Africa.
But to do this, several well-preserved samples from different
locations have to be studied.
Though human remains, particularly bones and teeth, can be found, the
DNA is very often degraded and is not suitable for undertaking complete
genome analysis. Moreover, contamination with modern human DNA should
not be present or should be only negligible.
Unlike in this case where the sample was preserved in permafrost,
cold conditions were absent in Africa, south Asia and Australia,
especially in the last few thousand years.
The next challenge To study samples that have not been deposited in
permafrost will be the next challenge.
"Although undoubtedly challenging [studying samples not deposited in
permafrost], it will, if successful, take the emerging field of
palaeogenomics to yet another level," the scientists write.
- The Hindu
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