Can we be sure which mummy was the daddy? When a state-of-the-art DNA analysis of Tutankhamun and other ancient Egyptian royals was published last year, its authors hailed it as 鈥渢he final word鈥� on the pharaoh鈥檚 family tree. But others are now voicing doubts.
The analysis of 11 royal mummies dating from around 1300聽BC was carried out by an Egyptian team led by Egypt鈥檚 chief archaeologist . The project was overseen by two foreign consultants, of the EURAC Institute for Mummies and the Iceman in Bolzano, Italy, and of the University of T眉bingen, Germany.
The researchers used the DNA data to construct a family tree of Tutankhamun and his immediate relatives. The study, published last February in the Journal of the American Medical Association (), concluded that , that his parents were brother and sister, and that two mummified foetuses found in Tutankhamun鈥檚 tomb were probably his stillborn daughters 鈥� conclusions that have since become received wisdom.
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But many geneticists complain that the team used inappropriate analysis techniques. Far from being definitive, the study is 鈥渘ot seen as rigorous or convincing鈥�, says Eline Lorenzen of the Center for GeoGenetics at the Natural History Museum in Copenhagen, Denmark. 鈥淢any of us in the DNA community are surprised that this has been published.鈥�
Degraded DNA
, a molecular palaeobiologist at Royal Holloway, University of London, is also concerned. 鈥淚n my experience it is not very easy to get these results,鈥� he says. 鈥淚 can鈥檛 do it, and I鈥檝e spent a long time trying.鈥�
Zink and his colleagues used a genetic fingerprinting approach that involves testing variable regions of the genome called microsatellites, which are made up of short sequence repeats. The numbers of repeats vary between individuals, and by comparing the number of repeats across several microsatellites it is possible to work out whether or not individuals are related.
However, researchers rarely attempt this approach with ancient samples because the original DNA is likely to be degraded, and dwarfed by modern contamination. It鈥檚 more common to sequence mitochondrial DNA (mtDNA) 鈥� cells contain around a thousand times more copies of mtDNA than of genomic DNA, improving chances of finding large intact samples.
Zink and Pusch defend their choice, saying that they took extensive precautions to guard against contamination. For instance, they extracted samples from deep inside the mummies鈥� bones, and genotyped lab staff to rule out contamination.
Not deep enough
But others doubt the precautions were sufficiently rigorous. Robert Connolly of the University of Liverpool, UK, who carried out blood typing of Tutankhamun鈥檚 mummy in the 1960s, argues that it would be difficult to reach deep enough inside Tutankhamun鈥檚 thin, fragile bones 鈥� or those of the two fetuses 鈥� to reach uncontaminated material.
Lorenzen adds that many people 鈥� not just the Hawass team 鈥� have handled the mummies since they were first unwrapped. The authors should have tested non-human samples from the tombs as negative controls, she says.
To judge the quality of the team鈥檚 results, Lorenzen and others are asking for access to raw data not included in the Journal of the American Medical Association paper 鈥� but Zink is reluctant to oblige, fearing the data would spark 鈥渁 lot of arguing鈥� over technicalities.
However, Zink, Pusch and colleagues insist that they will soon be able to put any doubts to rest. They say they have also extracted the mtDNA that Lorenzen and others consider necessary for rigorous genetic analysis and are still working on the data. They hope to publish the results this year.
But the critics are still advising caution. 鈥淲hen working with samples that are so well-known, it is important to convince readers that you have the right data,鈥� says Lorenzen. 鈥淚 am not convinced.鈥�
