Michael Cooley's Genetic Genealogy Blog
8 April 2020

Big Y-700 Update for Pettit-Mellowes



Counties left to right: Perry, Muskingum, Morgan, Westmoreland

After more than forty years, the Pettits are still at the top of my genealogy wish list. While tapping my fingers over the conundrum during the late 1980s and 1990s, I published The Pettit Correspondent, the Pettit Letter, and hosted the PETTIT-L mailing list. But the greater family of my Joseph Pettet (c1815-1880+) remained allusive. The handful of surviving records tells us he was born in Pennsylvania, married in Muskingum County, Ohio in 1835, raised his family in Morgan County, Ohio and, in the 1850s, moved his wife and brood of ten children to Putnam County, Missouri where he probably died. Joseph's researchers had known for at least a hundred years that a Thomas Pettet (1764-1840+), a generation older than Joseph, relocated his large family from Westmoreland County, Pennsylvania to Muskingum County (Joseph's place of marriage) in 1819 where Thomas taught school. Tom's brother, Elijah, was dead in Westmoreland by 1799, but his three children were in the Zanesville region by 1815. Joseph grew up smack dab in the middle of the lot, many of whom, like himself, lived in Deerfield (Morgan County) and the bordering Portersville (Perry County), Ohio. This Pettet family has been sorted out almost to a tee, but not a single record is close to proving Joseph's parentage. Despite this awkward fact, researchers have long wanted to show that Joseph was descended from the much earlier Thomas Pettit (married to Christian Mellowes) who immigrated from England to Massachusetts in the 1640s. ("Not so fast" was one of the premises of TPC. After all, we had no idea who Joseph's parents were.) But not so fast, Michael. We now have the genetic record. The first hints arrived more than ten years ago.

A tester at the Pettit DNA Project (now blocked to public view by its administrator) recorded his earliest known ancestor (EKA) as William Pettet (1805-1885), a proven son of the above listed Thomas of Pennsylvania and Muskingum County, Ohio. Remarkably, his Y-DNA profile matches with those testers descended from early Massachusetts immigrant, Thomas Pettit. And late last year, a Pettet cousin, a descendant of Joseph's son, Solomon Pettet, tested to have the same Y-DNA markers — those of teacher Thomas Pettet, the Ohio emigrant, and of Thomas Pettit the Massachusetts immigrant. Without getting into more detail, it's now nearly certain that Joseph was William's youngest brother and one of the nine children of Thomas of Zanesville. Likely, Joseph was one of Thomas's two children mentioned in this 1905 passage regarding the 1819 emigration. It was transcribed for the very issue of The Pettit Correspondent: "The entire party, except Mrs. Pettet, her baby and one boy who was lame, walked the whole distance."1

Thomas Pettet's father, Elias Petit (-1794) — probably Joseph's grandfather — is similarly elusive. The record places him only in Pennsylvania, which is one of the reasons I long declined on the suggestion that he was of the Thomas Pettit / Christian Mellowes lineage. But we now know that Elias's descendants have a matching Y chromosome. Serious consideration is now due to the old idea (never before mine) that Elias was of the well-studied New Jersey descendants of Thomas and Christian of which multiple Eliases can be counted. My long Pettit journey isn't fully in the bag, but it's closer than ever.


~~~

At the close of 2018, I wrote the aptly titled Pettit / Mellowes Y-DNA Profile, and in January of this year I created the (appropriately titled) Pettit-Mellowes Y-DNA Project on Facebook. This updates the project's members on the latest Y-DNA findings. Their tests not only rekindled my interest, they have provided glue for the other Pettit / Mellowes lineages — not necessarily in determining the identities of previously unknown fathers, but by proving that the testers actually belong to the same family. The three G's (genealogy, genetics, and geography) will help give shape to some of the blanks and even aid in some coloring.

FTDNA's Big Y-700 product looks at 700 STRs, described later, and about fifteen million SNPs. Each SNP is a single-letter mutation to one of the three billion genetic bases found in the human genome. Newly-discovered SNPs (novel variants) are deemed unique to the tester (at least for now) while the vast majority of known SNPs are arranged in a tree of SNP groups known as haplogroups. The further up the tree the older it is, and the older the haplogroup the more descendants it will have.2

Our Pettits are descended from a haplogroup of twenty-two SNPs known as R1b-BY200368. Here's a summary of the SNP results for our five Big Y testers.


Big Y tested descendants of R1b-BY200368

Here's the same data in tree format.


SNP Tree


The SNPs (Single Nucleotide Polymorphisms) shown above, are single units of DNA (or bases) that have mutated. For example, a guanine (G) molecule might have been replaced with a thymine (T) molecule, conventionally noted as G>T. Such mutations occur at the creation of a man's gamete cells (sperm). The happy cell that carries the male sex gene (which is located on the Y chromosome) and merges with an egg, will be present at the birth of all the couple's son, the "founder" of that SNP lineage. And from there, the Y propagates inside the trillions of cells though cell division, including his own gamete cells. In other words,

Father gamete (Y) + egg = son w/new SNP

To be clear, not all men are born with a new SNP on the Y chromosome. It happens only once every several generations. But they do inherit all the markers the father had. It must also be noted that not all SNPs are born equal. Some are born in volatile regions, areas of the Y that have a tendency to mutate frequently. Those SNPs should be noted but not counted on. Those born in stable regions of the Y will continue to propagate down the male lineage for as long as the lineage continues — hitchhikers to the future. I call them silent witnesses to history.


~~~

STRs (Short Tandem Repeats), on the other hand, are fickle. The same markers can regularly mutate. Unlike single-base SNPs, STRs are comprised of short strings of bases that repeat X number of times in tandem (near) to one another. For example, I have 34 repeats of TTTC at a region called DYS449. But it's the number of repeats that matters and, especially, the number of differences among those numbers between two or more testers. These two non-Pettit testers, despite having the same surname, are not related. For twelve markers, related male lineages will have no more than a genetic distance (difference) of 1. This example shows a total GD of 7.


Tester 1
Tester 2
GD
132415101113121210131130
132414111114121211131329
--111--1-21

Men having zero differences in the first twelve markers could have hundreds and more matches, which renders the matches nearly useless. They might have to go back two thousand years or more to find a common ancestor who will not, of course, be found in the genealogical record. The following, however, examines more than 700 STR markers. In the case of DNA, the more markers tested the better, and the more participating testers, the merrier. Simply put, more data means better analyses.

Although the Pettit / Mellowes group has only five Big Y testers, each one has several hundred sequenced STR markers. FTDNA's Big Y-700 guarantees at least 700 high quality markers. To achieve that number, the company tests 838 markers. Comparing #873086 to #261925, we find they share successful testing of 731 markers and mismatch on 14 markers, typically represented as 14/731 (about .02%). To put everyone on an equal footing, I've extrapolated the results to a common denominator of 838, the number of tested markers. In other words, 14/731 = 16.0/838. The GD is rounded to the nearest whole number.

Kit #B388754 is not listed in the following for two reasons: He's an exact match to his son, #891469, and has had only 500 STR markers sequenced. That could somewhat skew the numbers. And the two, because of their relationship, look like a single person (that is Y-DNA-wise). Statistically, it's prudent to treat them as such.

This table represents the genetic distance (the number of non-matching markers) between the testers.


Genetic Distance over 700-plus Markers



Here's a somewhat more visual representation. Again, the numbers refer to the number of mismatched markers. And remember, this is the count out of 838 tested markers.


And that roughly corresponds to the following tree. But please note this: To equate genetic distance with the number of generations is dangerous and should not be tried at home. SNPs are routinely placed on a guesstimate timeline because the complete SNP data set (at least for the Y-500) averages to about one SNP mutation every 144 years or so, which is probably rarely true on a case by case basis. It can never be taken to the bank. If such a study has been done on Y-STR genetic distance, I'm unaware of it. So, with crossed-fingers and under the threat of being humiliated, this kind-of sort-of works out in this small study: Imagine a one to one ratio between distance and generations. In this case, it does serve as a good illustration.

Count up from one of the testers to the common ancestor and back down to the second tester. There's an approximation of the GD. For example, this method matches in the case of the two Pettit/Gallagher testers, descendants of Samuel Pettit Jr. It also matches the number of generational differences between the Gallagher and Heath lines. Can we say that the mutual ancestor lived eight generations ago? Probably not, but it might not be far off.


STR Tree


There is one anomaly. There's a GD of 7 between kits #891469 and #261925 (Nathaniel versus Wiliam), but the genealogies don't align. That doesn't mean, of course, that the lineages are wrong. (After all, I've utilized some potential fakery here.) We simply have too few DNA samples. The Nathaniel Pettit and Elizabeth Heath lineage has, effectively, only one tester. And the William Pettit / Rebecca Clayton lineage has, in fact, one tester. Still, note that the STR tree corresponds to the SNP tree.


~~~

As mentioned, FTDNA's Big Y-700 looks at about fifteen million SNPs and at over 700 STRs. Big numbers. I hope these diagrams illustrate that further Big Y testing will provide more information regarding genetic distance. (Big numbers times many testers approach exponential growth.) However, Y-DNA testing can never replace good genealogy. After all, the names of our ancestors are not encoded into our genetics — we see only the remaining artifacts of their DNA. Nevertheless, this tree method suggests that the common ancestor of the first three testers could have been a rough contemporary of Nathaniel Pettit (1765-1849) and Abigail Wood, eight generations back from the father/son pair of #891469. And it's not too far out to suggest that these tested groups might share Nathaniel Pettit (1646-1718) and Mary Bailey, one of the Pettit / Mellowes sons. But, really, it's too early to judge.

Look at the sparse tree at Patrilineal Descendants of Thomas Pettit and Christian Mellows. We can easily recognize what "nodes" are useful for testing, specifically Thomas Pettit Jr (1640-) and another son of Pettit / Bailey. There are similar examples in all the trees at Pettit Patrilineages. In time, the SNP tree will begin to include other branches in the manner illustrated above — the degree of relatedness between Samuel, Nathaniel, and William. There might be no end to the complexities.


PETTIT/BAILEY DESCENT

Thomas Pettit (1609-c1668) m Christian Mellowes
Nathaniel Pettit (1646-1718) m Mary Bailey
Nathaniel Pettit II (c1676-1768) m Elizabeth Heath
George Pettit (1719-1775) m Susannah Heaton
Nathaniel Pettit (1765-1849) m Abigail Wood
Josiah Wood Pettit (1807-1870+) m1 Harriet m2 Mary Ann Brellhart
Andrew Jackson Pettit (1830-1908) m Jane Jackson
John Charles Fremont Pettit (1857-1937) m Mary Hoy
John Andrew Pettit (1882-1960) Alice Fisher
Ralph Joseph Pettit (1908-1988) m Mary Kenney
Kenney Joseph Pettit (1940-1974) m Lora Alice Davis
Living father Pettit
Living son Pettit

1 First published in an unknown newspaper in Perry County, Ohio, 1905. The article was in celebration of Lovey (Pettet) Hearing's 96th birthday. She was a daughter the Ohio immigrant, Thomas Pettet. The article states that the party walked about 200 miles. Today, the driving distance between Derry, Pennsylvania and Zanesville, Ohio is about 170 miles.

2 Haplogroups are simple enough but a clear definition is not easy. For now, imagine that each father-mother node on your genealogy chart is a haplogroup. Each family that descends from that haplogroup is a subclade, which in turn may become its own haplogroup. Therefore, the number of subclades and subsequent haplogroups tend to increase. However, as any genealogist knows, lineages often "daughter out." As it happens, my paternal grandfather's Y-DNA will disappear with the deaths of his five grandsons. Still, it serves to imagine that 5th great-grandparents will have more descendants than our parents presently have. And so the population boom continues.