Often, at least at the current stage of genetic genealogy, DNA sequencing does not reveal enough information to identify a personâ€™s particular Y chromosome or mtDNA haplogroup. The example I will be using in this post is Haplogroup E. Haplogroup E split into E1, E2, and E3 about 28,000 years ago. Current tests offered by many sequencing companies are able to place a person in the general â€œEâ€ Haplogroup, but might be unable to determine exactly which subclade of E a person descends from. In such a situation, a â€œDeep SNPâ€ test can be used to fill in that information.
A SNP is single nucleotide polymorphism, or a change in the DNA sequence at a single nucleotide. For instance, the switch of a C for G, a cytosine for a guanine. You can see a chart of some of the most common SNPs tested for genetic genealogy here or here. The Deep SNP test (which can go by other names) analyzes a personâ€™s DNA, such as the Y chromosome, for the presence or lack of these mutation(s).
Each SNP is detected either by sequencing or by cutting the DNA with enzymes â€“ the presence of a certain mutation will cause the enzyme to cut the DNA differently, either stopping it from cutting or allowing it to cut. The scientists can then analyze the results and determine whether or not the person has that particular mutation. Certain marker results will lead the person to be group in the haplogroup containing other people who have similar results.
Haplogroup E, for instance, is characterized by the mutation M96. If a person has this mutation, they would be M96+, it is extremely likely that they are directly descended from the founder of Haplogroup E. If they do not have the mutation, they are M96-, and they belong to another haplogroup. It isÂ helpful to follow along on the ISOGG Haplogroup E Tree.
Haplogroup E split into E1, E2, and E3 about 28,000 years ago. E3 is characterized by the SNP mutation P2, meaning that people who test positive for P2 (i.e. P2+), then it is extremely likely that they are directly descended from the founder of Haplogroup E3.
E3 split into E3a and E3b about 26,000 years ago. E3b is characterized by the SNP mutation M35. From Wikipedia: â€œE3b is believed to have first appeared in the Horn of Africa approximately 26,000 years ago and dispersed to the
So, therefore, if you belonged to subclade E3b, your Deep SNP test results would be (M96+, P2+, M35+). And E3b splits into even more subclades, meaning that you would have more SNP results.
Anytime you get Deep SNP results and arenâ€™t sure how to interpret them, use the ISOGG Haplogroup Trees. The identifying SNP for each branch of the tree is listed right next to the branch. ISOGG updates the Haplogroup Tree yearly, and even includes source information! Itâ€™s a great resource for genetic genealogists.
By the way, this post came about after a great email conversation with Tim at Genealogy Reviews Online. Thanks Tim!