What We Can Learn from Genetic Testing
In the last decade, the use of DNA testing as a tool for genealogical research has become both popular and controversial. As more people have expressed a desire to use scientific analysis to verify and augment their family trees and the cost of testing has become increasingly affordable for many, the number of companies and the varieties of tests offered by them have grown dramatically. Below is a synopsis of what kind of information we can ascertain from these tests and what their limitations are. In a follow up article, I will address how the frequently misunderstood and unknown parameters of these methods have led some to question the tendency to place undue reliance on their conclusions.
Broadly speaking, there are three types of DNA tests that can be used for tracing ancestry: autosomal DNA, mitochondrial DNA and Y-DNA.
Autosomal DNA (atDNA) is available for men and women and scans over 700,000 genetic markers on all 23 chromosomes to identify links on both maternal and paternal sides. The benefits of this test are its capacity to locate genetic cousins on any of the test takers’ ancestral lines and provide some information about ethnic composition. But atDNA testing can only identify shared ancestral information for about five to seven preceding generations. Thus, it is not useful for conducting research on more remote generations of relatives.
Mitochondrial DNA (mtDNA) is used to determine one’s direct maternal line. This category of DNA, which can also be used by both men and women, is passed onto male and female children by their mother and does not comingle with other genes. Therefore, your mtDNA will be identical to that of your mother, and your mother’s DNA will be identical to that of her mother and so on. Because of the relative stability of this DNA over years, if two individuals have an exact mtDNA match, it is likely they are both offspring of the same maternal ancestor. However, this test cannot determine how long ago that common maternal ancestor lived, so it may be difficult to ascertain how far back one needs to search ancestral lines.
Y-DNA tests are unique among these analyses because they can only be used by males to trace one’s direct paternal line. The Y chromosome, which only males carry, contains tiny markers that create a pattern called a haplotype. The composition of this haplotype is used to identify one’s family members. The primary weakness of this test is that common makers can only demonstrate a relatedness between two men and not the exact nature of the relationship.
The data these tests can provide is indicative of the enormous benefits of scientific and technological advancements in the field of genealogical research. Undoubtedly, for individuals seeking information about their origins who have minimal knowledge or available data, or limited access to living relatives, such testing has many useful applications. It is important to recognize though that the information you obtain from DNA testing is general and based on statistical probabilities. The misstep in such scientific research is not qualifying the resulting information, which often is the source of mistaken assumptions.