Frozen mummy?s genetic blueprints unveiled

The 5,300-year-old Iceman had brown eyes, Lyme disease and modern-day Mediterranean relatives

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By peering deeply into the DNA of the mummy known as ?tzi, geneticists have expanded the rap sheet on the 5,300-year-old Iceman: He had brown eyes, brown hair and blood type O, was lactose intolerant and his modern-day relatives live on Corsica and Sardinia.

These vital statistics and more come from an analysis of the Tyrolean man?s complete genetic blueprints, reported online February 28 in Nature Communications. The DNA analysis also found that the Iceman, found frozen and well-preserved in the Alps in 1991, carried genetic risk factors for heart disease. And he was infected with the bacterium that causes Lyme disease, making him the oldest known case of the disease.

For the new study, researchers led by Albert Zink, an anthropologist at the European Academy of Bolzano in Italy, removed a bit of ?tzi?s hip bone and extracted DNA from the sample. The mummy?s fresh-frozen state helped preserve his DNA, making deciphering a complete of set genetic blueprints easier than for most ancient samples, says Niels Lynnerup, a forensic anthropologist at the University of Copenhagen. ?It is much better DNA than you can get from one dry old bone,? he says.

?tzi?s brown eyes and lactose intolerance are evidence that scientists are right about the pace of evolution of some human traits, says John Hawks, an anthropologist at the University of Wisconsin?Madison. Mutations that gave rise to blue eyes and the ability to digest dairy products into adulthood arose sometime within the past 10,000 years but took multiple generations to spread throughout Europe.

People living in ?tzi?s time ?had the dairy animals, but what they didn?t have was enough generations for the gene to become common,? Hawks says. The finding that the Iceman was lactose intolerant confirms that picture. ?We were right about this gene. It is new.?

Previous studies of ?tzi?s genetic past examined DNA only from cells? energy-making factories, called mitochondria. People inherit mitochondria from their mothers, so that genetic material can be used to trace a person?s maternal lineage. ?tzi?s mitochondria carry some genetic variants not seen in modern Europeans, leading scientists to think that his maternal line has died out.

In the new study, researchers examined all of the Iceman?s DNA, including his Y chromosome. Since Y chromosomes are passed from father to son, certain molecular signatures on the chromosome can help identify relatives from the father?s side of the family. ?tzi?s Y chromosome contains genetic variants that are rare in Europe today, and found mainly in people who live on the islands of Corsica and Sardinia.

That doesn?t mean that the Iceman isn?t related to present-day people from the southern Alps where he lived and died, Zink says. Scientists don?t have DNA samples from many people in the Tyrolean Alps with which to compare ?tzi?s DNA, leaving open the possibility that researchers may yet discover other modern-day relatives, he says.

?tzi is the first ancient person ever diagnosed with Lyme disease, an infection caused by the bacterium Borrelia burgdorferi. Researchers have known that the bacterium has infected animals for millions of years and thought that ancient humans probably contracted the illness as well.

?It has been a theory that it goes back many, many thousands of years, but we?ve not had proof before,? says Allen Steere, a physician and scientist at Harvard Medical School in Boston who first discovered and named Lyme disease. ?This is proof that it goes back at least 5,000 years, and probably a long time before that.?

Found in: Genes & Cells and Humans

Source: http://www.sciencenews.org/view/generic/id/338822/title/Frozen_mummy%E2%80%99s_genetic_blueprints_unveiled

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