Geneticists at the University of Arizona have discovered the oldest known genetic branch of the human Y chromosome, the factor in DNA that determines male sex.

The discovery happened after an African American man living in South Carolina submitted his DNA to the National Geographic Genographic Project (NGGP).

None of the genetic markers used to assign lineages to known Y chromosome groupings were found so the NGGP passed the DNA sample onto Family Tree DNA, a company specializing in DNA analysis to trace family roots. They got to a dead end when they identified a lineage that didn’t match anything on the known Y chromosome tree.

Eventually researchers at UA found a match in the Y chromosomes of 11 Mbo men from a small region of western Cameroon in sub-Saharan Africa.

“Our analysis indicates this lineage diverged from previously known Y chromosomes about 300,000 ago, a time when anatomically modern humans had not yet evolved,” said Michael Hammer, an associate professor in the University of Arizona’s department of ecology and evolutionary biology and a research scientist at the UA’s Arizona Research Labs. “This pushes back the time the last common Y chromosome ancestor lived by almost 70 percent.”

Anatomically modern humans begin to appear in the fossil record about 200,000 years ago in East Africa.

One theory to emerge from these results is that there may be “pockets of genetically isolated communities” that preserve genetic information yet to be discovered. New discoveries could very well extend the age of the Y chromosome tree.

Y chromosomes are important in the study of genetics because the majority of a Y chromosome doesn’t exchange genetic material with other chromosomes making them more useful for tracking down ancestral roots.

“There has been a lot of hype with people trying to trace their Y chromosome to different tribes,” Hammer said, “but this individual from South Carolina can say he did it.”

Research findings were published in The American Journal of Human Genetics.