Post by zarahan on Sept 26, 2013 11:10:29 GMT -5
http://download.journals.elsevierhealth.....97308000859.pdf
Archaeogenetic Evidence of Ancient Nubian Barley Evolution from Six to Two-Row Indicates Local Adaptation
Abstract
Background: Archaeobotanical samples of barley (Hordeum vulgare L.) found at Qasr Ibrim display a two-row phenotype
that is unique to the region of archaeological sites upriver of the first cataract of the Nile, characterised by the development
of distinctive lateral bracts. The phenotype occurs throughout all strata at Qasr Ibrim, which range in age from 3000 to a few
hundred years.
Methodology and Findings: We extracted ancient DNA from barley samples from the entire range of occupancy of the site,
and studied the Vrs1 gene responsible for row number in extant barley. Surprisingly, we found a discord between the
genotype and phenotype in all samples; all the barley had a genotype consistent with the six-row condition. These results
indicate a six-row ancestry for the Qasr Ibrim barley, followed by a reassertion of the two-row condition. Modelling
demonstrates that this sequence of evolutionary events requires a strong selection pressure.
Conclusions: The two-row phenotype at Qasr Ibrim is caused by a different mechanism to that in extant barley. The
strength of selection required for this mechanism to prevail indicates that the barley became locally adapted in the region in
response to a local selection pressure. The consistency of the genotype/phenotype discord over time supports a scenario of
adoption of this barley type by successive cultures, rather than the importation of new barley varieties associated with
individual cultures.