SINCLAIR DNA CAITHNESS 

Extensive DNA testing has been done for the Surname Sinclair. Through testing it has been determined that there are some 23 or more different Haplogroups or types of DNA within the Surname, NOT ONE related to another.

DNA Haplogroup for Caithness is as follows
 
R-FGC15254 .......  which is a SPECIFID marker for Sinclair only. In other words you can have a different Surname but if you have that marker then your actually a Sinclair descendant. Many different reasons why the Surname could change, adoption, child taking his mothers name, simple change of name, illegitimate child.

So there you have it NO we are not all cousins, not at all. We can all still share the Surname and belong to the Social groups called CLAN Sinclair but most DO NOT share the History of the name . It has been determined that this is the exact case for ALL Scottish Surnames, and in Fact all Surnames Scottish or not 

Check out FAcebook pages for Sinclair and Please Join

Clan Sinclair Family
 https://www.facebook.com/groups/118259336835143 

Clan Sinclair DNA Mythbusters
https://www.facebook.com/groups/267128666703548 

Sinclair DNA Macts and Fiction 
https://www.facebook.com/profile.php?id=100064348553389