Genetic genealogy projects come in several flavors: surname, geographic, haplogroup, etc. Here we will focus on projects that involve a surname. Most involve Y-DNA testing involving men who are in the patrilineal line of descent from a progenitor of the surname. Patrilineal refers to an exclusive father to son lineage. The Y chromosome is what genetically distinguishes men from women. Every man gets his sex determining Y chromosome from his father. And since there is only one Y chromosome, it is passed undiluted through each generation. This makes it very valuable for genealogists. Science has created maps, based on occasional mutations, that can trace a man's Y chromosome back to Adam. The haplotree is created by connecting the novel mutations that define a new branch of the human tree (see figure, courtesy of Georg Dunkel).
We'll keep things relatively simple here and expand on specific issues in later blogs.
Several resources are available to support surname projects. This blog will focus on Family Tree DNA (FTDNA), which has excellent tools to support a project. You must first have a "kit" or Y-DNA test yourself or on one of your male kin. Then you can either join or manage a project. When you join a project, the administrator will look at your Y-DNA results and try to assign it to a group within the project. This arranges men who share common markers.
There are two kinds of markers used in Y-DNA analytics and shown in the illustration. Short tandem repeats (STRs) are shown as columns, with names such as DYS393. STRs are areas of the genome where sequences of DNA are replicated; the number of repeats is shown in the chart. The other marker is the haplogroup, shown in its own column. The haplogroup is defined by the most recently known mutation in a single nucleotide polymorphism (SNP). A polymorphism is a variation of a segment of DNA involving a single nucleotide. These mutations are less frequent, making them useful for looking further back in a lineage. In contrast, STRs change more rapidly, making them helpful in seeing variations within a group.
The illustration shows the SNPs forming the branches for the top group (green row). The individual tests have different haplogroup values, but notice that each one is defined by a SNP that is in the same path. So, these men are all on the same branch.
How is this useful? Genetics is a tool that augments historical record research. Each of the men in the top group had prior research showing their most distant known ancestor. Notice there are two who are in Ohio. Because of the results of other testers, they ordered a test for R-Z25289, which turned out to be positive. This pushed them farther out on the haplotree branch and indicates their kinship is much closer to others with R-Z25289. So we can conclude that the Ohio, South Carolina and North Carolina lines have a common ancestor after the time when R-Z25289 branch occurred. The timing of when a branch occurs is done by scientists using statistical methods, beyond the scope of this blog. Times are shown in the cover illustration of this blog as brown numbers between the SNP nodes; some are well within the time of historic records (300-500 years ago). R-Z25289 is much older, but surname projects create new information (novel SNPs) that will be used to define new branches that evolved more recently. These new data may also put individuals in a group into separate groups, helping genealogists refine their research.
We will pick up this discussion in subsequent blogs, but hopefully this gives you a high level of understanding of a surname project.