Deep Ancestry

Genetic genealogy can tell us about the deep ancestry of our ancestors and, in some case, which tribe or sept our ancestors came from. This story addresses the deep ancestry of Peter and Marilyn Carroll Biggins and their family through the use of Y-chromosome DNA, tested by Family Tree DNA. Y-DNA is passed down from father to son, much like surnames. By testing a living male, we can learn about the deep ancestry of his paternal line. Testing can also help determine how closely two people are related.

Let's go back to basics so that anyone rusty is back up to speed. :)

• Mutations occur in our genomes over time as genetic code gets copied.
• On the Y chromosome, mutations get passed from father to son.
• Because new mutations continuously occur, we can use the number of mutations that differ between two men as a relative measure of how far back in time they are related: the more SNPs that differ between them, the further back in time their common ancestor lived.
• We can group people sharing sets of mutations into haplogroups. Normally, this is done using Y-SNP mutations, because they are more stable. Each haplogroup is therefore defined by one or more SNPs, and contains two or more men. For example, the haplogroup R-A7373 is currently defined by ten SNPs and contains ten men.
• These haplogroups are effectively large family units, representing the male-line descendants of their common ancestor.
• Each man therefore belongs to a series of nested haplogroups, stretching from the global haplogroup that includes all mankind at one end, down through progressively smaller and younger haplogroups that contain fewer and fewer men, until eventually we can list the "private" mutations that are found only in that man's line and no-one else's.
• As new testers come along, they will form new haplogroups with the people they are most closely related to.
• In some cases, they will share some but not all of the SNPs within a haplogroup with the other testers.
• For example, an 11th man may come along who is positive for six of the SNPs within R-A7373 and negative for the other four. In that case, the haplogroup would split: an older, larger haplogroup would be formed with 11 men and defined by four SNPs, and a younger haplogroup would be formed with 10 men and defined by six SNPs. If the man was A7373+, then the younger haplogroup would retain the R-A7373 label. If the man was A7373-, then the older haplogroup would retain the R-A7373 label. In either case, the other haplogroup would then be named after one of the SNPs that define it.
• Not all sequencing tests are identical. There are differences between any two BigY tests of a few percent in coverage (and between BigY-500 and BigY-700 tests by about 33%).
• This means that sometimes some SNPs can be called in one test, but they may not appear in another test, or may appear with too low a quality to be clearly called.
• Sometimes, these SNPs may end up on the haplotree anyway, if they can be securely called among enough tests in the group. For example, most of us are Z2265+ and BY30097+, but that may not show up in all of our tests, because these SNPs are often called with low-quality results.
• SNPs are named by the lab that discovered them. For example, A-series SNPs were named after Thomas Krahn's lab at YSeq where we've done a lot of individual SNP and SNP-pack testing; FGC-series SNPs were named after the Full Genomes Corp., which re-analysed a lot of the raw files from early BigY tests. Family Tree DNA have several labels: BY-series SNPs refer to SNPs discovered in the original BigY-500 tests, while FT-series SNPs refer to SNPs discovered in the new BigY-700 tests. MF refers to the Chinese company 23mofang.