So, you have made a lot of progress on your family tree and you ask, “What can DNA testing do for me?” 

In this short essay, I won’t answer your question by delving into the fascinating details of DNA testing, as it is a complicated story and there is plenty on the subject available via the Internet. Suffice it to say that the fundamental principle is that DNA tests identify unique variations in your DNA, and use computer algorithms to identify others who share your variations, thereby establishing that they are your relatives.

But this being a Jewish journal, I will answer your question with a question: “What are you trying to learn?”  

To start that conversation, let’s discuss the three types of tests available:

• Autosomal tests, which decode a sizable portion of the X chromosome and the 22 non-sex chromosome pairs found in common among all human beings. This test may identify the existence of a blood relationships back roughly five generations.

• Y chromosome tests identify the male patrilineal lineage with a fair amount of specificity, from the near present back to the Stone Age; and

• Mitochondrial tests, identify the general matrilineal lineage of both men and women for thousands of years;

About the tests:

Autosomal

If you are trying to learn whether the person you met at the last week’s JGS meeting is a cousin, or if you are fishing to discover living relatives, or if you have no idea what your background is, then an Autosomal DNA test is for you.

If you and another person share meaningful segments of your autosomal DNA, you may possibly be related to one another in the last five generations. I say possibly because there has been so much cousin marriage within the Ashkenazi population that predictions based on autosomal results may appear much closer than they are. The fact is, the study of autosomal DNA is an art so once you get your results, start asking for help from one of the many mavens who can be found in your local JGS, on Facebook and at conferences. For testing, I recommend FamilyTreeDNA or MyHeritage as these have the largest databases of Jewish participants willing to communicate with matches.

Y DNA

If you are trying to learn whether your Slomowicz family is related to the Slomowicz that you played cards with last week, then a YDNA test by men in each family carrying the Slomowicz surname is the way to go. 

The test is male-specific because it identifies the male lineage that has been passed down for thousands of years from father to son.  In addition to sorting out surname relationships, one’s YDNA is a superb tool for learning about your patrilineal ancestors, including where they came from and when they joined the Jewish people, whether it was in Bronze-Age Israel or Iron-Age Iberia.  There are important projects going on right now among academics using the Y chromosome to learn about Jewish origins. To start out, I recommend the Y37 test from Family Tree DNA but there is advanced testing available in the form the Family Tree DNA BigY test, which uses the latest technology to scan millions of DNA locations to identify genetic variations that are unique to your lineage. I recommend that you start on your YDNA journey by joining the Avotaynu DNA project at www.JewishDNA.org and that your purchase your Family Tree DNA tests through their portal. To learn more, visit www.AvotaynuOnline.com.

Mitochondrial DNA

If you are trying to learn whether two individuals descend from a single common female ancestor, run a mitochondrial DNA test. Like YDNA testing, Mitochondrial DNA traces a direct lineage, albeit of the female line rather than the male line. Among Ashkenazim, many of these matrilineal lineages date back to antiquity in the Middle East, and others are of European origin dating back to the founding of the Ashkenazi population a millennium ago. If you are interested in exploring your mitochondrial DNA, I recommend the Mitochondrial Full Sequence test from Family Tree DNA.

Common Questions

Once you receive your results, it is perfectly respectable to find yourself scratching your head over their meaning.  Let’s look at some of the common questions:

• You have thousands of autosomal matches, some impossibly close:  Autosomal tests among Ashkenazi Jews often overstate the degree to which people are related because of our small founding population, restrictions on marrying outside the tribe, and extremely common cousin marriage. Marriage between cousins increases the amount of DNA that they share and makes them look inaccurately close. This includes the not-infrequent situation when cousins married and did even known that they were related. In other words, if matches look impossibly close, they probably are.

• You have thousands of autosomal matches and have no idea what side of your family they come from: consider testing cousins from different sides of your family to see if it is possible to divide the matches into paternal and maternal categories.

• Ethnic predictions based on autosomal results from different testing companies do not match one another: Ethnicity predictions at the various testing company may differ because each company has its own collection of test results that it uses for reference. ­­

• On a YDNA test you find a male with a shared surname, but you have no idea how closely related you may be: consider adding an autosomal test, and possibly a BigY test.

• On a YDNA test, your results show no close matches: consider a high- resolution BigY test to explore if you represent a new branch in the Jewish genetic family tree. 

• Your YDNA results do not match those of a man with the same surname from the same shtetl: Consider an autosomal test, as surnames were quite changeable in the old country, even within the same family, and you may well be related through one of your other branches. 

• You have different surnames, your relationship unknown, but you are a perfect DNA match: you clearly share a male common ancestor, most commonly before the adoption of surnames at the dawn of the 19^th Century. Consider a BigY test to help determine when the two families diverged.

In addition to personal genealogical research, what can I do with my results?

If you tested with Family Tree DNA, I recommend that you join your kit to the AvotaynuDNA Project by logging in your kit at www.JewishDNA.org and pressing “join”.  The Project is working with the Technion in Israel and Jewish historians around the world to catalog all known Jewish lineages and explore their histories, and its administrators offer free helpful advice.  I cannot emphasize how important it is for you to work with other genealogists who have DNA expertise. This is a fast-moving field with many new tools available and there is no written resource that matches the comprehensive knowledge of a mentor. Seek expert help wherever you find it.