I am co-admin for the Ross surname YDNA project at FamilyTree DNA. One of our project members genetically matches four men with McRae surnames by YDNA. So, I collected their YDNA test information and constructed the following chart to visualize their relationship: Ross-McRae Chart
Their common ancestor is calculated to have lived around 1550 AD. Two of the McRae men appear to be very closely related to each other. Also, the age of the relationship between all of the McRae men is the same as between the Ross man. In other words, none of these men appear to have adopted their surnames significantly prior to the others. So, from what I can tell, they likely descended from a common ancestor that may not have adopted a surname, but whose descendants did some times after 1550 AD.
Clan McRae is fairly large and well known within the Scottish Highlands. I was also curious to better understand the relationship of these McRae men to the core of Clan McRae. Here is the Clan McRae Core Chart from several dozen related men that comprise the largest single group and who have 111 STR data publically available.
Notice that the core of Clan McRae is extensive and extremely old. Their common ancestor is calculated to have lived around 1100 AD. This is long before surnames were commonly in use. Also, there are many men that are genetically related to the Clan Core, but who have adopted other surnames.
Here are the various adopted surnames: Campbell, Kimsey, MacMillan, McKenzie, McLennan, Moen, Munro, Napier, Naydock, Ogilvie, Oglesby, Shore and Stewart.
Notice that none of the men within the Core of Clan McRae have adopted the Ross surname, but they have adopted other common Scottish surnames.
So, I read some material about the McRae Clan and learned that the name means "Son of Grace". Historically, they did not have a Clan Chief, but were close allies of the MacKenzie Clan and fought in many battles.
At this point, I'm not too sure of what else can be safely concluded about the subgroup of Ross-McRae men. Obviously, they are both common surnames in the Scottish Highlands and probably lived their for centuries. The lands of Clan MacKenzie, where most McRae's probably lived are in Ross.
Anything else that I'm missing?
Thank-you!