STEWART STUART (royal) Y DNA Project - News

Written 2015/Sept/01

Why Big Y Tests Are Far Better Than Y-DNA111, etc. STR Tests.

The goal of all genealogists is to identify their ancestors and kinfolk as cheaply and reliably as possible. Big Y or FGC test are the best way to accomplish this goal. The results of SNP tests are far more trustworthy, reliable and cheaper indicators of one's genetic relationships to one's kinfolk and to EVERYONE else on earth than are STR test results (see ISOGG's tree at

Every branch of a family will benefit if at least one of its members orders a Big Y or FGC test in order to discover its terminal SNPs. You may respond to the 21/Aug/15 post at if you disagree.

Table # 1 below shows both Y-DNA111 markers and some of the results of the Big Y tests of the DNA of some of the descendants of Scottish hero Sir John Stewart of Bonkyll. He died about 716 years ago (on 22 July 1298 at the Battle of Falkirk ). All of his patrilineal descendants (and only they) test positive for SNP S781, a branch of R-L746 . Their FTDNA project is at .

The tables below show some of the results of this Stewart family's:

  • Extremely useful $575 Big Y SNP tests (as low as $425 during a holiday sale). These Big Y tests were ordered because their slightly less expensive Y-DNA111, etc. STR tests failed to accomplish their genealogical goals.
  • Far less useful $359 Y-DNA111 STR tests.

Hardly any off-modal STR marker values that could be used to distinquish one branch of Sir John's descendants from another (and from any of the other branches of the descendants of the first High Steward of Scotland) were discovered via the results of their Y-DNA111 STR tests.

Since Big Y tests include 495 STR markers, members who order them are over four times as likely to find shared off-modal marker values that distinquish their branch from the others. A few of these "branch" STR markers are shown in colorized Table # 2 below. SNPs are so much more useful than STR markers that nobody may be interested in any of these 495 STR markers.

The trouble with STR marker values is that they are too unstable (mutate back and forth too frequently) to provide much useful information about the branches to which very distantly related cousins belong.

In the tables below:

  • Colored cells in rows with ID numbers contain off-modal marker values.
  • A marker's location in FTDNA's five Y-DNA111 panels is indicated by the colors of cells in the rows that show the names of the STR Markers.

What Is a Branch Off-Modal STR Marker Value?

"Branch" off-modal STR marker values indicate that members of a patrilineal family belong to the same branch. Very few "branch" STR marker values can be found amongst the many shared off-modal marker values shown in Y-DNA111 Table # 1, e.g.:

  • The two listed members of branch A1a03 have NO off-modal marker values in common at the Y-DNA111 level.
  • The three listed members of branch A1a05 have NO off-modal marker values in common at the Y-DNA111 level (that two of them share DYS710=37 may be because they are such close cousins).

Some cousins have the same off-modal marker values due to random mutations, not because they belong to the same branch, e.g.:

  • Branches A1a02, A1a05a, and A1a07 have DYS540=12 in common even though they do not belong to the same branch.
  • Branches A1a02, A1a04 and A1a07 have DYS710=35 in common even though they do not belong to the same branch.
  • Branches A1a01 and A1a04 have DYS557=15 in common even though they do not belong to the same branch.

Guessing which off-modal STR marker values are "branch" markers may therefore:

The results of STR tests are not totally useless, e.g.:

  • Y-DNA67 STR test results reliably indicate to which of the many patrilineal families people with the surname Stewart belong.
  • Most men who can genealogically trace their shared patrilineal ancestors have almost identical STR test results. That 53238, 251918 and 148693 have FIVE off modal STR marker values in common at the Y-67 level shows that they belong to the same branch (A1a02) of Sir John's descendants (see Table # 4 below). Any Stewart who has some of the same off modal STR marker values as 53238, 251918 and 148693 may be able to prove that he belongs to this branch via a $17.50 test for SNP A5026 instead of via FTDNA's Big Y test.
  • Approximately fifth cousins E16164 and E15052 have four shared SNPs and three shared off-modal STR marker values at the Y67 level (few cousins who know that they are this closely related are likely to order two Y-DNA111 STR tests, two Big Y tests, and an $850 Elite Y test to boot)!
  • Men who have the same surname and different patrilineal ancestors are not likely to have identical STR test results (at the Y-DNA12 level, and especially at higher levels).