FREQUENTLY ASKED QUESTIONS
Regarding Y-chromosome Testing for Genealogy
Return to: Johns Family DNA page
DNA
DNA is the material inside the nucleus of a cell that carries genetic markers. There are some markers that are shared by some direct male descendants in a given family line.
DNA has four (4) base types. They are Adenine (A), Cytosine (C), Guanine (G), and Thymine (T). These always occur in base pairs of Adenine with Thymine (AT) or Cytosine with Guanine (CG). The sequence and repetition of these two base pairs is the basis for Y-chromosome testing.
Y-chromosome
The Y-chromosome only occurs in males. It is passed down from father to son. Also, this inheritance of Y-chromosome is generally passed down without any alteration. There can be minor variation but extremely little. Therefore, a male may have the same Y-chromosome as his great great-grandfather following directly back in his father’s line. (i.e. son to father grandfather to great-grandfather to great great-grandfather).
It is this unique genetic heritage that can help prove or disprove a close relationship between males with the same surname (paternal lineage).
Y-chromosome Testing
Segments of DNA on the Y-chromosome can be identified by location. These markers are noted by international convention by a designated number (DYS#).
The markers repeat many times on the DNA. The number of time the repeats occur varies and enables some sorting between males likely to be closely related versus those who are probably not related.
The Test – what it does and does not do
The test is a simple Saliva test (NO BLOOD!). A laboratory sends out a kit with swabs for taking saliva from the inside of your cheek. The participant sends the Saliva sample back to the laboratory for the Y-chromosome test.
What the Test Does Not Do
The Y-chromosome test has little meaning on its own.
What the Test Can Do
Rather than give some hypothetical example. I will use the specific example that has prompted our delving into DNA and the Johns family.
EXAMPLE: In our research we have found that Henry Johns (1757-1833) was probably related to a John Johns (1754-1835) who lived next to him in Shelby County, Kentucky in the late 1790s. Unfortunately, no documents have been found to prove this connection. However, if Henry and John shared the same father, they would have the same Y-chromosome. Henry and John would pass down the same Y-chromosome to their sons, who would pass down their Y-chromosome to their sons, etc. As a result, testing the Y-chromosome DNA in males directly descended from these two ancestors will probably have the same Y-chromosome and would help prove that Henry and John were brothers. If they were brothers, it may even help us find out exactly who was Henry and Johns father.
The Results
The test varies in the number of markers tested: 12, 25, etc. When exact matches are found, the people with matching markers probably had a common ancestor. The more markers that match increases the probability that the common ancestor was in the recent past (i.e. with an exact or almost exact match on 12 markers you may have a common ancestor in the last 14 generations; with the same match on 25 markers you may have the common ancestor in the last 7 generations).
Using this information in conjunction with standard genealogical research can help prove family connections.
EXAMPLE: In our study, a match or very close match between direct male descendants of Henry’s line and John’s line would virtually prove they were very closely related and probably brothers. However, if they do not share the same Y-chromosome, then they were just neighbors sharing the same surname. As you can see, this can profoundly effect the direction of research.