The following post is NOT an endorsement by the New Mexico Genealogical Society of FamilyTreeDNA.com or any other type of genetic genealogy testing site. It only offers options for the reader to consider regarding genetic genealogy.
On the New Mexico Genealogical Society's Facebook Page, we have been have been discussing Y-DNA results. FamilyTreeDNA.com and other similar companies have tests in which men can test their Y-DNA against others to see if they are closely related. Only men can do this test because only men have the Y chromosome. The Y chromosome is the thing that makes men male - women have two X chromosomes instead of an X and a Y. However, women can have their brothers, fathers, grandfathers, or uncles and cousins who are on the same paternal line take the test for them.
The great thing about the Y-DNA test is that it often shows the relatedness of individuals along the paternal line, which is the line that we often get our surnames from. The Y-DNA test shows the DNA of one's father's, father's, father's, father's, father, etc. Since this is passed on from father to son with little change, we can compare our DNA to people who may be our relatives within a few generations and see if we match with people who have the same or similar surnames as us. Sometimes people don't match. This might mean that one of the two people in the comparison might have a female ancestor who had a child with someone other than her husband, or an ancestor may be adopted, or an ancestor took on his mother's name rather than his father's.
What is a surname, anyway?
It's my opinion that surnames are arbitrary anyway. Western Europeans have been using surnames for only about 500 years, with a few going back further. Even then, many families named their children after grandparents who were not along the direct paternal line. For example, Cristobal Baca, the first Baca who came to New Mexico with his family in 1600, had daughters by the names of Juana de Zamora, Isabel de Bohorquez, and Maria de Villanuevo. Spanish explorer Alvar Nunez Cabeza de Vaca (no relation to the other Baca) took his mother's surname rather than his father's because it was more prestigious. I find through my own research that many surnames in New Mexico seem to become standardized by the middle 1600s. However, that's only about 350 to 400 years ago. If we look at each generation being approximately 25 years, we're only talking about 14 to 16 generations. Not much at all.
To add to the confusion, there were many adoptions in New Mexico. Because of war, disease and general bad health, parents sometimes died early. Children were raised by uncles and aunts and other relatives. Sometimes they kept their names, sometimes they took their adopted parents names. In addition, many household had Native American slaves who they adopted. These people often took their slave owner's surnames as their own.
However, a Y-DNA test might be helpful in solving some genealogy problems. I have two of them in my own family tree. The first is that my uncles claim that my great-grandfather Juan C. de Baca y Luna was adopted. They say that we are not actually Bacas. The other is that I'm not too sure about my genealogy past my fifth great-grandfather Juan Antonio Baca. Does it continue straight along the Baca paternal line, or does it veer off towards Josefa Baca, who had children out of wedlock and gave them her last name? I'm closer to answering the 1st problem, but I'm waiting for some responses from other people to try to answer the other. For more information on my quest, read my blog post.
Which Y-DNA test to take
There are five options for Y-DNA testing on FamilyTreeDNA.com: 12, 25, 37, 67, and 111 markers. The more markers, the higher resolution of the test. With higher resolution, you are able to more directly pinpoint how closely two individuals are related to each other. However, both individuals can only compare at the lowest common resolution. For instance, if one person took the 67 marker test and another took the 37 marker test, the resolution will be only as high as the 37 marker test.
Many New Mexicans have ancestry that goes back 12 to 14 generations in New Mexico. Because of this, I believe that 12 marker tests do not have enough resolution to accurately pinpoint someone who is related within that timeframe. According to a chart on the FamilyTreeDNA website (link), a person with an exact match of 12 markers on a 12 marker test has a 50% probability of being related within 7 generations, 90% probability of being related within 26 generations, and 95% probability of 29 generations. If two people only match 11 markers out of 12, the 95% probability goes up to 47 generations. I have people who match me perfectly who have Irish roots. Since my haplotype is Celtic, that's not a surprise. However, the separation between the Spanish Celtiberians and the Irish Celts is over 2,000 years!
25 marker test are better, but not good enough. The same chart shows that someone who matches 25 out of 25 markers is 50% likely to be related within 3 generations, 90% likely to be within 10 generations, and 95% likely to be within 13 generations. This is not close enough within the 12-14 generation timeframe.
37 marker test are probably good enough for most New Mexicans. A perfect match has a 50% probability of 2 to 3 generation separation, 90% probability of 5 generations, and 95% probability of 7 generations. If you are off by one marker, 50% to 95% go from 4 generations to 10 generations. Most people who are close matches to me have taken the 37 marker test. However, if you wish to get a little bit more resolution, try the 67 marker test.
If you are an exact match on the 67 marker test, the 50% to 95% probability range is 2 to 6 generations; off by 1 and it's 4 to 9 generations and off by 2 it's 6 to 14 generations. Many people testing in New Mexico are using the 67 marker test.
Although the 111 marker is an option, I actually believe that it is unnecessary for most New Mexicans. Not many people who have tested have used this option.
I hope this discussion helps out with any questions you may have about Y-DNA testing.