"Somewhere, something incredible is waiting to be known" Carl Sagan
sábado, 29 de octubre de 2011
Evolution - Iceman leaves few relatives
The Neolithic mummy dubbed the Iceman likely has no relatives alive today on his mom's side of the family, finds a new study of the ancient guy's genes.
Genetic material from the Iceman mummy suggests this Neolithic man has no modern-day relatives on his mom's side of the family [Credit: Web]
The remains of the Iceman (also called Ötzi, Frozen Fritz and Similaun Man) were discovered accidentally in 1991 by German tourists in the Eastern Alps. Since then, a suite of tests has opened a window into the mummy's life and death. For instance, the Iceman was about 45 years old when he died; he was probably a hunter-gatherer while alive; he sustained a shoulder injury from an arrow and might have died from head trauma; and his last meal included unleavened bread and meat.
Now, researchers have fast-forwarded genetically from 5,300 years ago when Ötzi died to the present to look at whether his maternal lineage is alive and kicking. It's probably not.
The research team, led by Franco Rollo of the University of Camerino and Luca Ermini working at Camerino and the University of Leeds, extracted DNA from Iceman's rectum. They analyzed the genome of the cells' energy-making structures, called mitochondria.
"You only get mitochondrial DNA from your mother, and she gets it from her mother and so on, so it forms an unbroken link all the way back to the common maternal ancestor of all of us," said researcher Martin Richards of the University of Leeds.
The results showed that Ötzi fits in genetically with a particular group of living individuals who share a common ancestral DNA sequence. Over time, different individuals and groups can branch off from the main group, genetically speaking. Ötzi’s DNA belonged to a cluster of lineages whose members are still common throughout Europe today.
However, nearly all members of this cluster belong to one of three sub-lineages, or sub-clusters. And Ötzi didn't. His DNA placed him on a completely distinct, fourth sub-lineage, for which there are no other members alive today — at least none have been found so far. His lineage branched away from his nearest modern relatives about 20,000 years ago.
That means Ötzi's maternal lineage is either extremely rare or has died out.The finding is detailed in this month's issue of the journal Current Biology.
The results run counter to past research by Richards and his colleagues, which suggested Ötzi's relatives still exist today in Europe. But the past studied relied on just a short segment of the mitochondrial DNA, unlike the recent study in which the entire mitochondrial genome was analyzed.
With less genetic material, as in the first study, fewer mutations show up. It's these mutations that scientists match up across the genomes of a group of individuals to say whether the group has a common maternal ancestor.
With more genetic material, as in the recent study, more mutations show up. And if scientists do find a match between different individuals based on those mutations, there is more certainty that the match-up is real and not some artifact of sampling or just due to chance, Richards said.
While the mitochondrial DNA findings suggest no modern-day Iceman relatives along his maternal line, the results say nothing about whether the Iceman had children, which would only have mitochondrial DNA from their mom.
In addition, the number of individuals with sequenced mitochondrial DNA is limited. That means there's a possibility individuals not in the database could hold mitochondrial DNA that matches up with that of the Iceman. Next, the researchers hope to continue their search for modern-day relatives of the Iceman.
"It would be nice to go and look in the areas where he might have grown up and see whether maybe there is some valley which has lots of related lineages to him," Richards told LiveScience. "That would be very interesting, because it would pin down where he or his family and his ancestors lived in much more detail than we can do at the moment."
The research was funded by global pharmaceutical company Eli Lilly and Co.