Tuesday, 24 November 2015

Genotyping a 500-year-old Inca child mummy.

In recent years the development of methods for sequencing ancient DNA has led to a greater understanding of how many ancient peoples are related to modern populations, particularly in Europe. However the method has been little used in the Americas, and in particular few studies have been carried out on Native American remains.

In a paper published in the journal Nature: Scientific Reports on 12 November 2015, a team of researchers led by Alberto Gómez-Carballa of the Departamento de Anatomía Patolóxica e Ciencias Forenses and Grupo de Investigación en Genética, Vacunas, Infecciones y Pediatría at the Universidade deSantiago de Compostela, describe the results of an analysis of a seven-year-old male child mummy from Cerro Aconcagua in Argentina.

The child was killed in an Inca 'capacocha' ritual, in which children of both sexes were sacrificed similtaneously throughout the Inca Empire on holly days or in response to events such as volcanic eruptions, droughts, earthquakes, battles or the deaths of Emperors. The Incas extended their empire from Peru southward into Chile and Argentina between 1438 and 1533 (when the last Inca Emperor, Atahuallpa, was executed by the Spanish Conquistador Francisco Pizarro), giving a time of death for the child constrained to within a century.

The Aconcagua mummy. The inset shows a picture of a portion of dissected lung from the mummy. A small piece of 350 mg was used for DNA extraction. University of Cuyo in Gómez-Carballa et al. (2015).

Gómez-Carballa et al. examined the mitochondrial DNA of ttissue taken from the lung of he mummy in order to assess its ancestry. Because mitochondrial DNA is found in the mitochondria, organelles outside the cell nucleus, it is passed directly from mother to child without being sexually recombined each generation, enabling precise estimations of when individuals shared common ancestors, at least through the female line (it is also possible to trace direct ancestry through the male line, using DNA from the Y chromosome, which is passed directly from father to son without sexual recombination).

The mummy was found to belong to the C1b haplogroup (a haplogroup is a group of individuals shown to share a common acestry through the male or female line, using either mitochondrial or Y chromosome DNA). This is one of the most common Native American haplogroups, and is also known from some very ancient American remains. The common ancestor of all people with the C1b haplogroup is thought to have lived between 20 400 and 16 200 years ago, either in Beringia (the area of land connecting Alaska to Siberia, which was exposed during the last ice age when sea-levels were much lower) or in the earliest settlements in North America, though the C1b haplogroup appears very early in both Central and South America, suggesting that the group of people in which it was found expanded southwards very rapidly.

The C1b haplogroup is divided into a number of clades (a clade is a group of organisms defined by haing a common ancestry), but the Inca mummy cannot be placed within any of these. Instead it is placed in a new clade C1bi, where i stands for 'Inca', which appears to have branched from its closest relatives around 14 300 years ago. The closest previously described clade to C1bi is C1b13, though all members of this group are thought to have shared a common ancestor about 11 800 years ago, so C1bi cannot comfortably be placed in this group. C1b13 is virtually absent from both North and Central America, and is most abundant in Chile, suggesting that the ancestor of this group lived in southern South America. This suggests that C1bi also bellongs to a lineage from southern South America, probably within the southern Andes. While this is the first individual discovered with this haplotype it cannot be inferred that the haplogroup is extinct or even especially rare; low sampling of mitochondrial DNA among living populations in the area means that potentially the haplotype could be very abundant today.

See also...

http://sciencythoughts.blogspot.co.uk/2015/04/late-pleistocene-lithic-artefacts-from.htmlLate Pleistocene lithic artefacts from the Bear Creek Site on the Puget Sound.                       The earliest Human settlers are thought to have entered the Americas across the Bering Straits during the last glaciation when sea levels were much lower than...
The Taíno people are thought to have colonized the Caribbean Islands by island hopping from northern South America from about 500 BC onwards, reaching Jamaica by around 645-898 AD. They were skilled agriculturalists, introducing crops such as Cassava and Maize from South America and changing...
The earliest people arrived in the Americas some time between 12 000 and 13 500 years ago. They are known from burials and tools scattered (albeit thinly) across both North and South America. Art made by these...

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