According to the genetic genealogy testing company BritainsDNA, about 50% of the 70,000 people who carry the surname Stuart or Stewart in the UK or Ireland descend from the Royal House of Stewart.

The company tested the descendants of James Stewart, 5th High Steward of Scotland (c.1243-1309) and his brother Sir John Stewart of Bonkyll (c.1245-1298), and found that people descending from the senior branch did not carry the S781 mutation, while those descending from the junior branch did. Si John Stewart had two sons, Sir Alan and Sir James, and descendants on both sides are positive of S781. In other words, the S781 SNP arose in Sir John Stewart of Bonkyll.

Sir Alan is the direct patrilineal ancestor of King James VI and I.

The S781 mutation is found downstream of R1b1a2a1a2c1i1 (L744/S388), itself descended from the DF13/S521 branch of R1b-L21.


BritainsDNA said that they were able to clearly distinguish between the four cadet branches of the royal Stewarts, namely:

- the Appin Stewarts
- the Lennox Stewarts (the direct ancestors of James VI and I)
- the Albany Stewarts
- the Moray Stewarts

The announcement was not very clear. It says that some17,500 Stewart/Stuart men in Britain and Ireland are of royal descent, although that is 25% of the total, not 50%.