Tikalon Blog by Dev Gualtieri

Parchment DNA

February 26, 2015

As Marshall McLuhan so famously stated, "the medium is the message." He reasoned that the medium influences the perception of content, and I notice that when I compare movies with the books on which they're based. Some scientists from Trinity College Dublin have taken this saying literally, as they have been examining DNA and protein from the parchment of documents written in the 17th and 18th centuries.[1-3]

Parchment is a writing material made from the skin of animals, such as sheep and calves. Parchment was used as a writing medium more than two thousand years ago. The Dead Sea Scrolls were written on ibex and goat parchment. Even after the widespread use of paper, parchment was reserved for important documents for which common paper was deemed too impermanent.

A parchment dated April 2-15, 1742, from Vicars Choral Estates.

(Trinity College Dublin Image, by permission of the Borthwick Institute for Archives.)

Parchment could be an invaluable aid in the study of the historical proliferation of livestock species, since there are millions of parchment documents in archives, and the parchments are closely dated to the manuscripts written on them. However, it's always been assumed that DNA analysis would be a challenge, since there would be cross-individual and cross-species contamination in the parchment preparation process in which many animal skins might have been washed, cured and depilated at the same time.[1] To assess the feasibility of such analysis, the Trinity College researchers applied DNA sequencing techniques to a seventeenth century and an eighteenth century parchment.[1-3]

The DNA analysis of these parchments established the type of animal, sheep, from which these parchments were made. Not only that, but these ancient genomes could be compared to those of their modern equivalents, thus providing a clue to the genetic diversity of these sheep over time.[2] Says Daniel Bradley, a professor of Population Genetics at Trinity College Dublin,

"Wool was essentially the oil of times gone by, so knowing how human change affected the genetics of sheep through the ages can tell us a huge amount about how Agricultural practices evolved."[2]

Parchment is an unique DNA reservoir, since, unlike bone remains, it has been carefully preserved above ground in a controlled environment.[1-2] Bone remains contain high levels of bacterial DNA and low levels of the DNA from whence they came.[1]

Small (2 cm by 2 cm) specimens were obtained from parchments at the Borthwick Institute for Archives of the University of York. These specimens were used for both DNA analysis and for mass spectrometric analysis of extracted collagen.[1-2] One parchment was linked to the black-faced breeds of northern Britain, while the other had a closer affinity with Midland and southern Britain where livestock improvements were common in the later 18th century.[2]

Histogram of raw sequence read alignments (see reference for color codes) that indicate a match to the sheep genome for one of the two parchments in the study.

(Fig. 1(a) from ref. 1, licensed under a Creative Commons Attribution License.)[1]

Says Matthew Collins, a professor in the Department of Archaeology at the University of York,

"We believe the two specimens derive from an unimproved northern hill-sheep typical in Yorkshire in the 17th century, and from a sheep derived from the 'improved' flocks, such as those bred in the Midlands by Robert Bakewell, which were spreading through England in the 18th century. We want to understand the history of agriculture in these islands over the last 1,000 years and, with this breath-taking resource, we can."[2]

Species localization map for parchment genome

A synthetic map of how the genome of one parchment matches the genotypes of modern breeds. "Warmer" colors indicate a better match.

(Fig. 2(b) from ref. 1, licensed under a Creative Commons Attribution License.)[1]

The number of archived parchments in the United Kingdom is estimated to be quite large. About 15 million sheep were slaughtered annually from 1150 to 1850. Estimating that 1% of these became parchment and only 4% of these parchments now survive, gives 4.2 million parchments, although even a lower estimate of a million would be significant.[1] This allows the possibility that historical genetic maps from a variety of domestic species can be assembled to document the last thousand years of animal breeding history.[1]

Parchment DNA

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