DNA Testing, Part 2 – Y-DNA Explained

In Part 1 I discussed autosomal DNA (atDNA), that DNA that is passed down equally from both parents. In Part 2 I discuss yDNA, the DNA chromosome that is passed down only from father to son .

The Y-Chromosome

The Y-Chromosome is a sex chromosome and defines maleness. Only males carry the Y-chromsome and they pass that chromosome to male children unchanged except for an occasional replication error. The Y-chromosome can go for thousands of years with only a few replications errors (mutations) – but these errors are critical in using yDNA for genealogical purposes. Because yDNA is passed down father to son, it is the most important test for those who are engaged in surname genealogical projects. My yDNA is essentially the same as that of my 10G grandfather Muncy. Almost the same, but not quite.

Replication Errors (Mutations)

When enough males are tested, a profile of the Most Recent Common Ancestor (MRCA) emerges. There are currently 111 markers in the yDNA test, and related individuals will almost always show excactly the same value in each and every marker — unless there is a mutation at that marker. For example if ten people take the yDNA test and 9 of the 10 males show a value of 14 at marker DYS444, then the modal value (14) becomes the assigned value for that marker of the Most Recent Common Ancestor. As future males are tested, they should have a value of 14 at that marker.

A very important fact is that when mutations occur, those same mutations are passed down to sons and grandsons and subsequent generations.  For example, if my great-great grandfather had a y-chromsome mutation that changed the value of the DYS444 marker from 14 to 15, then my father will have that value and I will have that value and my son will have that value. Yes, additional mutations can occur, but that mutation will remain until there is another mutation at that same location. By comparing the value of mutations and their locations, we can assign relationships. Unfortunately it takes a number of males tested to definitively decide when a mutation occurred. In my case, I know I have a mutation of 15 at DYS444, but I don’t know when that mutation occurred. It could have been my father or my GGG grandfather. More testing could nail it down, but based on known relationships with others who have tested, it is likely the mutation occurred in the mid-to-late 1700s, but not yet proven.

Unfortunately mutations are random and cannot be predicted. No errors may occur for hundreds of years, and then one or two replication errors might occur over the course of a few generations. However, frequent replication errors are the exception and the distance between generations can be averaged. Genetic distance is the combined number of mutations between two men and is used to detemine probablity of a relationship. For example, comparing two men who have taken a 67-marker yDNA test might show a genetic distance of 3 or 4, indicating they are related “and likely to share a common ancestor within the genealogical timeframe” although probably not a recent relationship.

In the U. S., the only company that tests y-chromsome DNA is Family Tree DNA (FTDNA). Please note that FTDNA tests only provide DNA data that will help in genealogical study. (Their tests won’t tell you if you will develop chronic ecema or irritable bowel syndrome in the future!) FTDNA not only tests but provides tools for matching and maintains an excellent database of matches. Once you test with FTDNA you receive a kit number and all matches are related to that kit number. With FTDNA  your only cost is the cost of testing. There are no annual subscriptions or user fees other than those costs of testing. That’s good news for those who look back at the YEARS of monthly subscription fees paid to other online genealogy companies.

The good news is no recurring fees. The bad news is that y-chromsome and mitochondrial DNA testing is expensive. Currently the yDNA basic 37 marker yDNA test starts at $169, with the 67-marker test priced at $268 and the 111-marker test at $359. These prices can change, and there is occasionally a sale price.

The most common advice is to start with the basic 37-marker test and upgrade if you think the additional marker levels will help. I guess that is OK advice, but I’m going to be straight with you. Once you get 37-marker results you will find that it doesn’t provide enought information to really be helpful so you WILL upgrade to the 67-marker test. The added upgrade cost means you will pay more to achieve the 67 markers than you would have if you had paid for the originial 67-marker test, and you will have spent months more waiting for results. In my case, I ordered the 67-marker upgrade the day I received my 37-marker results — AND I ordered an upgrade to 111 makers the day I received my 67-marker results. I ended up paying a lot more money. In my case the 67-markers ended up being important since my only mutation from the common ancestor profile was in the makers covered by that test.

My advice?  Start with 67 markers, and if you can afford it, go for the 111-marker package.

“That’s a lot of money!!” I can hear you say. Yes, it is. But you can lessen the pain significantly with a little ingenuity. Do you have brothers (and sisters)? Remember that only males can test the y-chromosome, but your yDNA is extremely likely to be identical to your brother(s). Why not make a family project out of the test and split the cost among siblings? When you consider the fact that everyone in the family will benefit from the genealogical information your yDNA test can give, the perceived costs drops greatly.

Having spent many years reading old documents, searching cemeteries, and trying to pull information out of forgetful relatives, I’ve come to recognize that DNA offers an enormous new tool in family research. It offers the promise of solving puzzles that we never dreamed could be solved. But it is only helpful if people invest in the tests, and the more data we have the better the results. If you are a male Muncy, please seriously consider the 67- or 111-marker yDNA test.  It’s really important for the future.

For more information and another explanation of the Y-Chromosome, I highly recommend Roberta Estes’ blog on the issue at DNAeXplained.

Leave a Reply