Friday, November 24, 2023

FamilyTreeDNA's Big Y-700 Uncovers Family Relationships

Genetic genealogy provided evidence that three men - all contemporaries who shared the same unusual name - were closely related to each other. But what exactly was the relationship between them?

My fourth great-grandfather was Vachel Kirk. He was born in 1805 in Ohio to Thomas and Sarah (Bonar) Kirk and lived in Licking County where he married Jane Delzell.

He was my family tree’s first Vachel. When I discovered two other men with the same peculiar name living in the same era and in generally close proximity, I had to take a closer look.
  • Vachel Kirk #2: Born in 1783 in either Ohio, Pennsylvania, or Virginia (his children couldn’t agree on a location), he married Rachel Hall. Records place him in Fayette County, Pennsylvania through 1815. Beginning in 1820, he appeared in Butler County, Ohio, where he lived the rest of his life.
  • Vachel Kirk #3: Born in about 1803 in Ohio, he married Susanna Allstaff. Records place him in eastern Ohio (Belmont, Harrison, then Morgan counties) from 1825 through 1850. In 1855, he moved to Hendricks County, Indiana where he lived the rest of his life.
Mindful of traditional naming patterns, I wondered if they were related.

Y-DNA Testing Establishes a Connection

A third great-grandson of Vachel Kirk #2 took an autosomal and Y-37 DNA test with AncestryDNA and FamilyTreeDNA respectively. The Y-DNA results indicated that he was a close genetic match to a dozen direct male descendants of Thomas Kirk, including his son Vachel. The autosomal test also surfaced more than a dozen matches with descendants of Thomas Kirk. However, the low levels of shared DNA make it difficult to pinpoint a specific family relationship with any certainty.

Encouraged by the initial matches, we upgraded the descendant’s Y-DNA test from Y-37 to Y-111 and then finally Big Y-500. At each level of higher testing, the matches with descendants of Thomas Kirk remained the closest.

In April 2023, I finally located several living direct male descendants of Vachel Kirk #3. One of the men, a descendant of Vachel’s son Isaac Kirk, agreed to a Big Y-700 test.

The results showed that he was a close Y-DNA match to all of Thomas Kirk’s descendants and the descendant of Vachel Kirk #2.

Finally, I had evidence that all three Vachel Kirks were indeed genetically related to each other.

Y-DNA Mutation Suggests Close Relationship

The Big Y results for the descendants of Vachel Kirk #2 and #3 suggested a particularly close relationship.

In fact, Vachel #2 and #3 are so closely related that both men belong to their own recently identified haplogroup, branching off from the haplogroup shared by Thomas Kirk and his descendants, including his son Vachel Kirk #1.

Y-DNA matches are defined by naturally yet random occurring mutations in the Y chromosome. These mutations are what allow us to distinguish Kirk men from any other man you pass on the street. They define our paternal ancestry. Men pass these mutations or haplogroup on to their sons which makes it possible for genetic genealogists to trace patterns of relatedness (source: David Vance).

Both Vachel Kirks have a newly identified Y-DNA mutation or haplogroup called R-BY100766 that is unique to them.

So why is this important and what does this reveal about my genealogy?

First, if Thomas Kirk (1778-1846) and Vachel Kirk #2 (1783-1836) were brothers (as I initially theorized), then the R-BY100766 mutation had to occur in Vachel #2 because Thomas’ descendants are negative for this haplogroup. 

However, if the R-BY100766 mutation occurred in a generation before Vachel #2 and he inherited it from his father, then he is NOT a brother to Thomas Kirk who is negative for the mutation.

Focusing on the relationship between Vachel #2 and #3, their shared R-BY100766 mutation suggests that they could be:

Father and son

Hypothetical father and son relationship for Vachel Kirk #2 and #3

Although the Y-DNA indicates it is a genetic possibility, a father and son relationship seems unlikely because Vachel #2 and his wife Rachel Hall eventually named one of their children Vachel in 1834 – over three decades after the birth of Vachel #3 (note that this child is not accounted among the three men referenced in this study). Why would Vachel #2 name two of his sons Vachel – especially if the first son of that name was still alive?

The father/son relationship theory is also undermined by the fact that Vachel #2’s future wife Rachel Hall was only 13 in 1803 when Vachel #3 was born. While not biologically impossible, it seems unlikely that she was his mother. There is currently no evidence that Vachel #2 had a relationship prior to Rachel Hall that resulted in children.

It may also be telling that there were just a dozen autosomal DNA matches between the descendants of Thomas Kirk and the descendant of Vachel Kirk #2. A previous case study examining siblingship between Thomas and Mary (Kirk) Geiger surfaced over 100 paired matches. The fewer number of matches between Thomas and Vachel #2 may be a sign that the relationship was more distant thus explaining the drop off in autosomal matches.

Because of the genealogical unlikelihood that Vachel #3 was a son of Vachel #2, it seems probable the R-BY100766 mutation was inherited from a previous generation, suggesting Vachel #2 and Thomas were not brothers.

A more likely relationship scenario is that Vachel #2 and #3 were:

Uncle and nephew

Hypothetical uncle and nephew relationship for Vachel Kirk #2 and #3

FamilyTreeDNA estimates that the most recent common ancestor of the R-BY100766 haplogroup was born around 1770 which they round down to 1750. Although not conclusive, this age approximation would fit well with the birth of Vachel #2’s father.

This would mean that the R-BY100766 mutation was inherited by Vachel #2 from his father (whose identity we don’t yet know). Vachel #2’s unknown father would then be the grandfather to Vachel #3.

In this theory, Vachel #3 would be the son of an unknown Kirk who was brother to Vachel #2.

What do you think? Does this seem possible to you?

Regardless of the scenario, to surface answers, our path forward will require more testing (both Y-DNA and autosomal). Thank goodness for Black Friday and Cyber Monday deals! 

We're getting closer to definitive answers. One cheek swab and saliva sample at a time.


  1. I like to think I'm an amateur sleuther myself. I had a 2nd ggf born in 1855 to a single mother and given her surname. I had a 1st cousin 1x removed take the Y-37 test hoping to get lucky to shed light on his paternity. It took me to the name Hoover. I searched my own Ancestry test for Hoovers. The closest match took me to a Hoover family that fit location/time and had many matches to this family. Turns out Herbert Hoover is my 4th cousin 3x removed. Was thrilled to let my cousin know he shares the same Y-Chromosome as a US President.

    1. It's pretty incredible the discoveries we're now able to make thanks to genetic genealogy. And who doesn't love a high profile connection? Thank you for reading and sharing your experience, Rae. I appreciate it!