If our ancestors and families had stayed in one geographic region and never moved outside of it, it would be relatively easy to distinguish their DNA (and ours), from the DNA of people living in other regions. Over time, the people of our region would come to share specific genetic mutations, which would identify them as a distinct population, just like a surname identifies members of a family. But, our ancestors did not stay in one area. For thousands of years, humans have moved around, leaving their genetic imprints wherever they procreated and making it difficult for geneticists to distinguish one region’s population from another’s. The important thing to remember is DNA tests can only estimate where in the world our ancestors originated.
To find out if we are the descendants from another male ancestor, you only have to turn to Y-DNA testing. The Y chromosome is passed virtually unchanged from father to son, just like (in most cases) a surname. So on the paternal side, our Great…Grandfathers should have the same Y-DNA as his son, his son, and so on. You can use Y-DNA to trace your paternal lineage, which is represented by the top line of a pedigree chart. Women do not have a Y chromosomes, a female wanting to research a descendant needs to turn to her biological father and his Y-DNA. A father, brother, uncle (father’s side), a male cousin (her father side), or even a nephew (her brother’s side) can all take the test to find out if they are part of their descendants.
Mitochondrial DNA (mtDNA) traces maternal lineage, which is on the bottom line of a pedigree chart. Mother’s pass their mtDNA to their daughters and their sons, but only daughters pass mtDNA on to the next generation. Surnames are usually not useful when looking at descendants on the maternal side.
Testing your own or a close relatives Y-DNA or mtDNA can reveal information about your paternal line (father’s father’s father) and your maternal line (mother’s mother’s mother) but not about anyone in between. The bottom line on our DNA testing is: Our (Paternal) Grandfather was born out of wedlock, with the father never being revealed; the Johnson line can not be used to prove any of our ancestors on the Johnson side. On the rest of the Family, the only other Male Grandparent was a Farrington, in this case we would need to have one of our related cousin a male Farrington to take the test and prove that side of the family. Riddle and Alexander were both our (Maternal) Grandmother’s families. We would need a female directly related to that side of the family to prove through mtDNA testing any of those ancestors.