But many geneticists complain that the team used inappropriate analysis techniques. Far from being definitive, the study is "not seen as rigorous or convincing", says Eline Lorenzen of the Center for GeoGenetics at the Natural History Museum in Copenhagen, Denmark. "Many of us in the DNA community are surprised that this has been published."
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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's more common to sequence mitochondrial DNA (mtDNA) – 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' bones, and genotyped lab staff to rule out contamination.
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But others doubt the precautions were sufficiently rigorous. Robert Connolly of the University of Liverpool, UK, who carried out blood typing of Tutankhamun's mummy in the 1960s, argues that it would be difficult to reach deep enough inside Tutankhamun's thin, fragile bones – or those of the two fetuses – to reach uncontaminated material.
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Lorenzen adds that many people – not just the Hawass team – 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's results, Lorenzen and others are asking for access to raw data not included in the Journal of the American Medical Association paper – but Zink is reluctant to oblige, fearing the data would spark "a lot of arguing" over technicalities.
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