Dorothy, Your two McCartys, William Thompson, and William W. McCarty belong to the genetic haplogroup, I2B1, that's(eye two, bee, one). The computer eyes and ones look so similar, I felt I needed to clarify that.The haplogroup I2B1 has a frequency in Ireland os somewherebetween 10 and 25 percent, which means that is some parts of the country up to 4 out of 10 people have this haplo-type. Today it's highest frequency is found in Norway and other parts of Scandanavia.What does that mean for you?Probably that your McCartys are of Viking descent.Does that mean, not Irish.Of course not!Ireland was not only pillaged by the Vikings, many of it's largest cities were founded by Vikings, e.g. Galway, Dublin, et. al.The Vikings married into Irish families along the western seaboard settlements, and many adopted the name of their Irish wives' families.Or, I'm sure left many an Irish girl pregnant, carrying sons with I21b1 genes.That's the way civilization and history hasworked.