Paleogenomics

The Nobel Prize for Physiology this year has been awarded to Svante Pääbo, Swedish geneticist, who pioneered the field of palaeogenomics, or the study of ancient hominins by extracting their DNA.

Read about it at : https://officerspulse.com/nobel-prize-for-physiology-medicine-2022/

Paleogenomics is a field of science based on the reconstruction and analysis of genomic information in extinct species.

Pääbo managed to sequence a region of mitochondrial DNA from a 40,000-year-old piece of bone. This was the first time a genome from an extinct human relative was pieced together. Subsequently, he managed to extract enough nuclear DNA from Neanderthal bones to publish the first Neanderthal genome sequence in 2010. This was significant considering that the first complete human genome was published only in 2003.
He also made the sensational discovery of a previously unknown hominin, Denisova.
Pääbo also found that gene transfer had occurred from these now extinct hominins to Homo sapiens following the migration out of Africa around 70,000 years ago

The challenge with extracting DNA from fossils is that it degrades fairly quickly and there is little usable material. The chances of it being contaminated by human as well as other bacterial DNA is higher. This has been one of the major stumbling blocks to analysing DNA from fossils.
DNA is concentrated in two different compartments within the cell: the nucleus and mitochondria, the latter being the powerhouse of the cell.
Nuclear DNA stores most of the genetic information, while the much smaller mitochondrial genome is present in thousands of copies and therefore more retrievable.

Pääbo’s most important contribution is demonstrating that ancient DNA can be reliably extracted, analysed and compared with that of other humans and primates to examine what parts of our DNA make one distinctly human or Neanderthal.
Europeans and Asians carry anywhere between 1%-4% of Neanderthal DNA and there is almost no Neanderthal DNA in those of purely African ancestry.
Comparative analyses with the human genome demonstrated that the most recent common ancestor of Neanderthals and Homo sapiens lived around 8,00,000 years ago.
In 2008, a 40,000 year-old fragment from a finger-bone, sourced from a Siberian cave in a region called Denisova, yielded DNA that, analysis from Pääbo’s lab revealed, was from an entirely new species of hominin called Denisova.
Further analysis showed that they too had interbred with humans and that 6% of human genomes in parts of SouthEast Asia are of Denisovan ancestry.
At the time when Homo sapiens migrated out of Africa, at least two extinct hominin populations inhabited Eurasia. Neanderthals lived in western Eurasia, whereas Denisovans populated the eastern parts of the continent.
During the expansion of Homo sapiens outside Africa and their migration east, they not only encountered and interbred with Neanderthals, but also with Denisovans.

The study of ancient DNA provides an independent way to test theories of evolution and the relatedness of population groups.
The Rakhigarhi(Indus Valley civilisation site) fossils showed that these Harappan denizens lacked ancestry from Central Asians or Iranian Farmers and stoked a debate on whether this proved or disproved ‘Aryan migration.’
Palaeogenomics also gives clues into disease. Researchers have analysed dental fossils to glean insights on dental infections.
Genome-wide association studies, where segments of DNA from species are compared, have found that Neanderthal DNA may be linked with autoimmune diseases, type 2 diabetes, and prostate cancer.

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