The man’s Y chromosome — a hereditary factor determining male sex — has a history that’s so old, it even predates the age of the oldest known Homo sapiens fossils, according to the report, published in the American Journal of Human Genetics.
The fellow’s chromosome turned out to carry a rare mutation, which researchers matched to a similar chromosome in the Mbo, a population living in a tiny area of western Cameroon in sub-Saharan Africa.
“Our analysis indicates this lineage diverged from previously known Y chromosomes about 338,000 ago, a time when anatomically modern humans had not yet evolved,” Michael Hammer, who worked on the study, said in a press release.
“This pushes back the time the last common Y chromosome ancestor lived by almost 70 percent.”
Hammer is 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.
The DNA detective work began after the South Carolinian submitted a small tissue sample to the National Geographic Genographic Project. The researchers were shocked after they noticed none of the genetic markers used to assign lineages to known Y chromosome groupings were found.
They sent the man’s DNA sample to Family Tree DNA for sequencing. Fernando Mendez, a postdoctoral researcher in Hammer’s lab, led the effort to analyze the DNA sequence. It included more than 240,000 base pairs of the Y chromosome.
Searches through a huge database led to the Mbo connection.
The scientists could then estimate the emergence of the chromosome mutation based on rates of change, creating a sort of “family tree” for the chromosome.
The discovery doesn’t necessarily mean that we all descended from an ancestor living in western Cameroon.
“It is a misconception that the genealogy of a single genetic region reflects population divergence,” Hammer explained. “Instead, our results suggest that there are pockets of genetically isolated communities that together preserve a great deal of human diversity.”
Read more at Discovery News
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