The Y and mtDNA Trees

What is the new Y Chromosome Tree?

The new Y-Tree is a chart of human paternal relatedness showing how all men’s Y-chromosomes lineages stem from an ancient male ancestor in Africa more than 150,000 years ago. Since the time of that common ancestor, his billions of descendants have journeyed around the world and in the process accumulated mutations in their own DNAs that make them and their paternal relatives unique. Each mutation marks a genetic event that occurred at a particular time and place in our shared ancestral journey. Today, all men carry in their Y chromosomes a series of DNA mutations that tell the story of humanity. The new Y tree is therefore the global genetic map of these known mutational events that show how we are all distantly or closely related.

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How did my Y Chromosome DNA help create the new Tree?

By joining the Genographic Project and opting into science, you allowed us to compare your anonymous DNA results to those of thousands of other participants. Next, we calculated your shared but also your unique mutations. The presence and absence of mutations in yours and other people’s DNA helped us better understand the order in which these mutations occurred. This final step helped us reconstruct the chronological steps in our shared human journey. In other words, if you shared 98% of your mutations with someone else, you shared a common ancestor with that person up until a specific moment in the past, or up to a specific point on a branch. Your unique 2% denote mutational events that are recent and therefore fall along tips of branches that distinguish you from that “relative.” The same analytical rules apply for the mitochondrial DNA tree.

What is the new mitochondrial DNA Tree and how does it affect my results?

Similar to the Y-tree, the new mitochondrial DNA (mtDNA) tree is a chart of human maternal relatedness showing how everyone’s mitochondria stem arose from that of an ancient female ancestor in Africa some 150,000 years ago. Since then, her billions of descendants have accumulated novel mutations in their mtDNA. Today, the mtDNA tree is a global map of shared and unique mutational events that charts how we are all closely or distantly related.

As technology improves scientists can sequence more mtDNA genomes, and as more genomes are sequenced new branches are discovered or “grown” on the shared tree of maternal ancestry. The Genographic Project is now using the most updated mtDNA tree available. This tree is known as Build 16 on Phylotree.

As new branches of the tree grow so may your haplogroup. For example, with the new tree we now can inform you that your haplogroup is not just J1c2, but it is more specifically J1c2o. So, for some people the new mtDNA tree increased the specificity of their particular haplogroup.

How different are the new DNA trees to previous versions?

With the new Y tree the number of branches nearly doubled, from 667 to more than 1200, and new connections and bifurcations since emerged. Haplogroup C, for example, changed form now showing patterns of relatedness among East Asians, Aboriginal Australians, and Native Americans. For the new mtDNA tree we added more than 750 new branches, nearly all of these branches were on the tips of the tree.

In general, the overall structure of the tree remained consistent with past versions, thus not affecting your major haplogroup designation (H, J, R, and so on). However, more branches mean greater geographic specificity – helping us narrow down where your haplogroup is found and when the haplogroup was born – and this is where you can play an active role in the scientific process.

What does this mean for my current results?

Your results may have changed as we gained greater resolution of migratory paths, we repositioned a few Y chromosome mutations along the journey, and we discovered new branch tips on both the Y and mtDNA trees. Your ancestral journey may have grown thanks to our new understanding of internal branching patterns of the tree and of events that occurred between 10,000 and 60,000 years ago as humans moved to populate every corner of the earth.