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University of Minnesota
February 6, 2012
"The Creation of Eve," a marble relief by Lorenzo Maitani, from the cathedral of Orvieto, Italy.
Students trace their sometimes surprising genetic ancestry
By Deane Morrison
You never know what you may find when you search your DNA for clues to your ancestry.
One student found that she shared a maternal line of descent with Russian royalty. Another was surprised to find that his or her (the student's identity is protected) maternal line went back to Asia.
This kind of hidden genetic diversity turned up in University of Minnesota biology students last fall during a weeklong lab exercise created by graduate student Hernan Vazquez Miranda. He was inspired by National Geographic's Genographic project, which is collecting data on genetic variations of humans worldwide.
"This was the first time anybody had looked at genetic diversity at the university level," says Vazquez Miranda. "It turned out that the class represented two-thirds of the world's human genetic diversity, so the U is a much bigger 'melting pot' than we suspected."
After swabbing their cheeks for cells, each student in the BIOL 3409-Evolution class extracted DNA from his or her mitochondria—the tiny energy factories inside cells—then made multiple copies of the DNA. After these samples were sequenced, the students analyzed their DNA.
"One mission of our course is to try to engage people who want to go into the health field in thinking about basic research," says Vazquez Miranda. "What's more interesting than knowing who you are?"
Students from the fall 2011 BIOL 3409-Evolution course.
Mitochondria are believed to have originated eons ago as bacteria that were incorporated into the cells of bigger organisms. They carry their own chromosome, and mutations in that DNA accumulate at a steady rate. Mitochondria in egg cells are passed from mother (never father) to child each generation; thus, they constitute a direct line of maternal descent.
At least 150,000 years ago, our human ancestors in sub-Saharan Africa went through a population bottleneck. Today, all people are descended from one woman, dubbed mitochondrial Eve, who lived then.
Tracing back to Eve
When mutations occur in mitochondrial DNA, they stay put on the chromosome and get passed down from mother to child over countless generations. Suppose 10 people all carried mutation A. But if only five also carried another mutation, B, then B must have occurred after A. Each mutation defines a haplogroup; here, haplogroup B is also a subgroup of haplogroup A. Tracing the historical sequence of mitochondrial DNA mutations around the globe, researchers have found a common, and therefore ancestral, haplogroup: mitochondrial Eve's.
Since mitochondrial DNA mutates regularly, scientists can calculate how long mutations have been occurring since "Eve's" day: at least 150,000, but perhaps well over 200,000, years.
When modern humans spread around the globe, mutations in mitochondrial DNA popped up all over. Groups of people with the same mutation(s)—called haplogroups—became associated with specific geographical areas of origin; 24 haplogroups are now recognized. They have been used, for example, to track migrations, as when haplogroups from eastern Asia were found in the Americas, the result of migrations over a transient land bridge that spanned the Bering Sea during the last ice age.
"The class gives a perspective on where—what continent—the maternal lines came from in the distant past," says Leah VandenBosch, who found she shared a haplogroup with ill-fated Czar Nicholas II and other members of Russia's Romanov dynasty. "I was surprised to be related to the Romanovs, but it was really no big deal."
Another surprise: "One person in the class was closely identified with me within a haplogroup, so much so that I expected that person to be Asian," says Bradford Clemens, whose mother is Filipina. "But I asked the other Asian students, and all said they weren't that person." Therefore, one of the non-Asian students—who chose not to come forward—has a maternal line stretching into that continent.
The anonymous student didn't necessarily have an ancestor who moved all the way from eastern Asia to another continent. More likely, a line of female descendants moved out of Asia over many generations.
Also, the person in the class whose haplogroup was most ancient—that is, originating in East Africa and closest to that of mitochondrial Eve—was of Asian Indian ancestry.
And of the 24 known haplogroups, 16 were represented in the Evolution class.
"This is a dimension of diversity that hasn't been explored," Vazquez Miranda says. "And this is in just one class at the U of M.
"If an alien came to abduct our class, it would have a good sampling of humanity."
Published in 2012