If your Sinclair DNA is showing the L21 SNP, then don't' be surprised if you see the name Kerr in your name matches. One of our Sinclair DNA L21 member shows a match with a Kerr on 33 out of 37 markers tested. Another member matches a Kerr/Carr participant on 103 of 111 markers. That is an extremely close match.
According to the author Bruce A. McAndrew, a cadet line of the St Clair family of Herdmanston held the barony of Cessford from 1376 to 1416.
The lands of Cessford are in the border region, about 13 miles north of Jedburgh Abbey.
Later, in 1450, powerful Cessford Castle was built here by Andrew Ker.
Did the Sinclairs leave their DNA here in Cessford?
Did a Kerr take the name Sinclair from the local St Clair land baron?
We don't have enough evidence to make a decision at this point.
Through more SNP testing and lots of records research, we hope to get the answers.