DNA and Genetic Genealogy
Clues to your past cannot only be found in the records at the library and courthouse, they can also be found in your genes. DNA has been used for many years to identify people, but in the year 2000, DNA testing for genealogical applications hit the commercial market. DNA testing is best used to help confirm a link where no conventional source records exist or, in some cases, to determine if a person is part of a larger group, such as the Jewish Cohanim lineage.
Genetic genealogy tests look at the variations in the sequence of DNA from one person to the next. The more closely two people are related, the more similar their genetic material, or genomes. What's interesting is that all humans are about 99.9 percent the same. It's in that other 0.1 percent that you find the genetic differences that make you unique. Every once in a blue moon a small change or “stutter” occurs in this unique portion of our DNA. This “hiccup,” or genetic mutation, is then passed down to a person's descendants. A similar mutation found in two people's DNA means that they share an ancestor somewhere in the past.
To help locate these genetic mutations, scientists have identified genetic markers, certain short segments of the DNA strand with known genetic characteristics. These markers which can be found at specific locations, or loci, on the chromosome are essentially places where the same pattern repeats a number of times. Since the number of repeats within these sequences is inherited, people who match at a number of markers are almost certain to share a common ancestor.
Will genealogy DNA testing reveal medical problems?
The markers analyzed in traditional genealogy tests are from noncoding DNA, or what is commonly referred to as “junk DNA.” These stretches of DNA have no known function and do not reveal anything about personal traits or medical conditions. Because genetic testing is so sensitive, most companies have strict policies in place to assure their clients that their DNA is kept private, and separate from any personally identifying information. Generally, most facilities assign a unique number to each DNA sample, and that number and the surname is all the testing lab ever sees.
A special type of marker known as a Short Tandem Repeat (STR) is the one most often used in genealogy testing. In general, a DNA testing company will offer several different levels of tests — twelve markers, twenty-five markers, thirty-seven markers, sixty-seven markers, and so on. Depending upon the number of markers tested and the number of matches, your results will also indicate with a certain degree of probability how long ago this common ancestor lived. It is best to test a minimum of thirty-seven markers to achieve any sort of meaningful result. Basically, the more markers you test, the more conclusive your tests will be. The cost also goes up as the number of markers goes up, however, so most people choose to test a moderate number of markers (in the twenty-five to thirty-seven range). Almost all testing companies keep your DNA on file for a specified number of years, and will allow you to test additional markers at a future date if you so desire.
Genealogy DNA tests do not tell people precisely how they are related, or who their common ancestor is. DNA tests also can't tell you about the large portions of your family tree that don't descend directly from father to father, or mother to mother, unless you pair this with traditional genealogy research to track down direct-line descendants of those ancestors and have them participate in DNA testing.
For genetic genealogy purposes, three types of DNA can provide useful information: Y chromosome, mtDNA, and autosomal DNA.
Paternal Ancestry — Y-DNA
Human gender is determined by the X and Y chromosomes, two of the twenty-six chromosomes carried in the human cell. Females have two X chromosomes and males have one X and one Y chromosome. When a child is conceived, it receives one sex chromosome from each parent. The chromosome from the mother will always be X, but the chromosome from the father could be either X or Y. A child who receives an X chromosome from the father will be a girl; receiving a Y chromosome will make the child a boy.
Because the Y chromosome is the only human chromosome not affected by the constant reshuffling of parental genes, the DNA present in the Y chromosome is passed down virtually unchanged for many generations. This means that every male directly descended from the same distant male ancestor will have an extremely similar pattern of Y-DNA markers, making the Y chromosome extremely useful to genealogists. Since the Y chromosome is only present in males, the popular Y-DNA genealogy test can only be done on males, however. If you are a female interested in your paternal line, you will need to find a male relative (father, brother, cousin, and so on) from that line to be tested.
When you take a Y-line DNA test, your results will come back as a string of numbers. These numbers represent the repeats (stutters) found for each of the tested markers on the Y chromosome. These results have no real meaning taken on their own. Instead, you compare your results with other individuals to whom you think you are related to see how many of your markers match. Matching numbers at most or all of the tested markers can indicate a shared ancestor. Depending upon the number of exact matches, and the number of markers tested, you can also determine approximately how recently this common ancestor was likely to have lived (within five generations, sixteen generations, and so on).
Additional information and collaboration resources for genetic genealogy are available from several online sources. The International Society of Genetic Genealogy (
Maternal Ancestry — Mitochondrial DNA
Just so the females don't feel left out, you have your own special DNA test as well. Maternal DNA, referred to as mitochondrial DNA or mtDNA, is passed down from mothers to their sons and daughters. It is only carried through the female line, however, so while a son inherits his mother's mtDNA, he does not pass it down to his own children. It does mean, how-ever, that both men and women can test their mtDNA.
The mtDNA mutates much more slowly than Y-DNA, so it is really only useful for determining distant ancestry. Your mtDNA results will generally be compared to a common reference sequence called the Cambridge Reference Sequence (CRS), to identify your specific haplotype, a set of closely linked alleles (variant forms of the same gene) that are inherited as a unit. People with the same haplotype share a common ancestor somewhere in the maternal line. This could be as recent as a few generations, or it could be dozens of generations back in the family tree. Your test results may also include your haplogroup, basically a group of related haplotypes, which offers a link to the ancient lineage to which you belong.
Autosomal DNA
Autosomal DNA is the DNA found in the twenty-two chromosome pairs that contain randomly mixed DNA from both parents, basically all chromosomes except the sex chromosome. Autosomal DNA contains almost the entire genome, or blueprint, for the human body — where you find the genes that determine your physical characteristics, from hair color to disease susceptibility. Because autosomal DNA is inherited by both men and women from both parents and all four grandparents, it can be used to test for relationships in all family lines — a potential goldmine for female genealogists and adoptees. As a genealogy application autosomal testing is fairly new, but 23andMe's Relative Finder (
A variety of DNA testing labs specialize in DNA testing for genealogy applications. FamilyTreeDNA (
While Y-DNA, mtDNA, and autosomal DNA are the most common genetic tests for genealogy, there are also other tests available for determining distant and recent ethnic origins.
To learn more about the various DNA test types and what you can expect from the results, try the GENEALOGY-DNA-L mailing list (
Use DNA Testing to Learn about Your Roots
DNA testing is easy and painless. Basically, you sign up with a DNA testing company and order the test in which you are interested. They will send you a kit with a cheek swab (or in some cases a mouth wash or spit tube) with which to collect your sample. No blood is collected. You then send back the kit containing your DNA sample. A few weeks later you'll get your results.
Join a Surname Project
Genetic testing for ancestral connections provides the most information when you have others with whom to compare the results. One of the best ways to do this is to join a DNA surname study in which men with the same surname compare their lineages and DNA test results to see if they are related. Women can play too, of course, but they'll have to find a direct-line ancestor with the surname to take the actual DNA test, as surname studies are based on Y-line ancestry. As an added bonus, many testing facilities offer a substantial discount to participants in group projects.
Many surname projects have their own website, so an Internet search such as crane dna or crane surname study may turn up just what you need. Be sure to search for variations of your surname as well (e.g., Crain, Craine, Crayne). For smaller or newly created projects, check the project listings at the various DNA testing companies. DNA Heritage (
Create a Medical Family Tree
Many health conditions, from cancer to high blood pressure, tend to run in families. Some of these diseases are purely genetic. Most, however, are a mixture of genetic makeup and environmental factors. In these cases, you are not born with the condition; you only inherit a susceptibility or predisposition to developing it during your lifetime. By tracing the health problems and diseases suffered by your parents, grandparents, and other blood relatives, you can learn about your possible inherited risks. This information can help you and your doctor take preventive steps to lessen your chances of acquiring the disease or condition.
The Internet offers a number of resources for anyone interested in tracing their medical family tree. Online tools and guidance are available, for example, on the website of the U.S. Surgeon General's Family History Initiative (
