As described on the Genographic Project's website, deep ancestry is identified through the analysis of two small and distinct segments of DNA known as mitochondrial and Y-chromosome DNA. Mitochondrial DNA (mtDNA) exists in every male and female alive today. It is a portion of DNA inherited strictly maternally. So your mother got it from her mother, who got it from her mother, who got it from her mother, and so forth, forming a deep and direct branch of strictly maternal ancestry. Because mothers pass on their mtDNA to both sons and daughters, the Genographic Project is able to identify a maternal haplogroup for every Genographic participant.
The Y chromosome, on the other hand, only exists in males: Each man inherited his Y chromosome from his father, who got it from his father, who got it from his father, and so forth, forming another deep branch of direct ancestry. However, since Y-chromosome DNA (Y-DNA) only exists in males, the Genographic Project is currently unable to identify a paternal haplogroup from a female’s DNA sample. Female participants eager to learn about the paternal ancestry would need their father, paternal uncle, or a full male sibling to submit a sample.
Regional Ancestry
Based on their different destinations, humans migrating out of Africa developed regional affiliations over time. Modern-day populations from around the world carry particular blends of regional affiliations. These affiliations are present as patterns of DNA and are visible today in the variety of physical traits humans possess. Scientists have identified typical individuals, genetically speaking, from different parts of the globe and defined them as “reference populations.”
The Genographic Project compares a participant's DNA results to 60 geographic and ethnic populations and calculates which two of these populations are most similar to a participant in terms of the genetic markers they carry.
Results are determined by analyzing small bits of DNA scattered across the entire genome. This portion of your ancestry comes equally from both parents, all four grandparents, all eight great-grandparents, and so forth. Unlike mtDNA and Y-DNA this portion of your DNA gets scrambled every successive generation, so what can be learned from it is not so much your deep history, but it does set of percentages that represents a rough estimate of how much DNA you share with various groups around the world.
The percentage of your DNA that comes from each of your ancestors drops by half as you go back through the generations—you inherited half of your genome from your mother and half from your father but only a quarter from each of your grandparents. Because of this, the ability to see regional ancestry decreases with each preceding generation. If, say, your great-grandmother (three generations removed) was 100 percent Native American, that would show up as roughly 12 percent of your DNA. The rough limit of the Genographic Project's results is six generations, or 64 ancestors, each of whose contribution is less than 2 percent. For this reason, the Genographic Project doesn’t identify regional percentages that are less than 2 percent in results, even when they do exist.
