A DNA Allegory

Many years ago, your ancestor, Elias Surname, had a treasured possession. It was a book given to him by his father and had indeed been handed down through many generations of Surname sons.

It was an odd book with strange text that he couldn’t decipher. Even though Elias was unable to read the book, he painstakingly copied its entire text, letter by letter, so that each of his two sons, Edward and John, could have one of their own, just as his father had done for him. It was also tradition that only natural-born sons were to receive copies of the Surname book.

Being human, people can make mistakes and Elias was no exception. An occasional ‘w’ may have looked like an ‘v’ or perhaps he read a ‘c’ as an ‘o’. Yet, Elias’ sons appreciated the effort of their father. When they grew to adulthood and had sons of their own, they too made near perfect copies to pass along, keeping the ones their father made for themselves.

Over time, Elias’ descendants grew in number and lost contact with one another, as families tend to do. Some men kept the family name as it always was while others altered it. Yet, all that time, the fathers dutifully made almost identical copies of their book to pass to each of their sons.

You have a copy of Elias’ book that was given to him by your father who received a copy from his father, and so on, back to Elias’ son, Edward. One important thing to remember is that you do not have the originals of Elias’ or Edward’s books. They took their books with them to the grave as has everyone else with a copy. The only versions you have access to are those copies belonging to living relatives with an unbroken father-son link back to Elias.

Recently, you’ve been able to read very specific words of your copy. Granted there are only eight of them and they are meaningless on their own. The chart below lists what is found on each page at a given word. For instance, assume the 4th word on page 864 is ‘grapd’ and the 30th word on page 12,557 is ‘pob’.

What is interesting is when you compare your book to your father’s brother. All eight words that you are able to read in your uncle’s book are identical to the ones in yours. Since you and your uncle have no differences that you’ve seen, you can assume that your most recent ancestor (your grandfather and your uncle’s father) had these same words in his book.

Through standard genealogical research, you have located another of Elias’ descendants. William Surnom, whom you believe may be a direct-male descendant from Elias’ other son, John. He has consented to read some words from his book and pass the results to you.

He reads the words at the same eight locations in his book and the results are interesting:

The eight words are the same as yours except for the 12th word on page 1835. While your book reads ‘wux’ his reads ‘vux’. As can be expected, somewhere, someone made a change in passing a copy to their son.

You and William Surnom are definitely related. What the results do not tell you is when that change occurred or even what the original word was. They also do not tell you exactly how you and William Surnom are related other than the two of you are fairly closely related at one word change apart.

A few months later, you are contact by a Thomas Surname who believes he is also descended from your Elias’ son, Edward Surname. His genealogical research is sound and he agrees to read some words from his book as well to add to your growing list of versions.

These words are wildly different from your family’s. The words are not just a letter off but are completely different. The only similarities are the 61st and 62nd words on page 3389. But during your research you have learned that most of the men from Elias’ home country have these two words unchanged.

You and Thomas Surname are not closely related at all. Since you have already confirmed the connection between yourself and another Elias relative, you can conclude that Thomas is not a descendent of Elias. Evidently somewhere in Thomas’ line something occurred. It could have been an adoption. It may have been a husband taking the family name of his wife. Whatever the reason, Elias is not the male-line biological ancestor to Thomas.

This analogy roughly details how genealogical genetic testing works and what you can learn from it. Y-DNA is like the book in that a copy is passed from the father to the son. Occasionally a change occurs during the transcribing process, leaving the son with a version slightly different than his father’s.

We can read select ‘words’ from our Y-DNA. The positions along the dna are not identified by page and word number but are given location names, such as ‘DYS 19’, ‘DYS 459a’ or ‘Y-GATA-H4’. The ‘words’ are not really words but numbers that represent a characteristic of the dna at that location. Through commercial testing, you can obtain the values of anywhere between 12 and 60 locations. In addition, the ‘words’ that are read are indeed meaningless, just as in the analogy. They come from sections of the Y chromosome that are ‘junk’. That is, they do not serve any purpose and thus pose no risk to disclose.

For instance, here is an example of my results:

Researchers have estimated the rate at which a given location may mutate. Using this, I can compare my results with those of other Whitehead/Whited researchers and get an idea for our degree of relatedness. The simple rule is the fewer differences between your results and that of another person with the same surname, the more closely related you are.

Genealogical genetic testing is used to reinforce your genealogical research but it cannot replace it. It can disprove a relationship, allowing you to avoid devoting effort to a false path. Yet it cannot definitively prove a relationship. It is simply another form of evidence for you to use.