DNA relatives

2015 was the year that DNA testing opened new windows on my family history research. Dee and I did autosomal testing with the three primary testing companies here in the United States. These tests produced long lists of prospective cousins who presumably share ancestors in common with us. Those potential cousins might have information that we don’t have about our ancestors. Coordinated research of shared DNA and traditional genealogy can reveal ancestry that we weren’t aware of.

Sometimes things aren’t as they appear. A DNA match might be a false call as a relative. Our chromosomes are comprised of DNA segments from different branches of our family trees with no signs marking their boundaries. A mixture of the DNA from both of our parents might match part of a segment from a single ancestor on someone else’s chromosome, giving the appearance of shared DNA from a single common ancestor. This is fairly common for small matching DNA segments. This DNA is identical by chance (IBC), not identical by descent (IBD) from a common ancestor. You might also see IBC segments referred to as identical by state (IBS). Many prospective DNA relatives who share very small segments of DNA with us are not in fact our relatives.

On the other hand, the fact that you don’t share DNA with another tester doesn’t mean that you are not distantly related. Our cells contain 22 pairs of autosomal chromosomes, one of each pair from each parent. For example, we have a pair of Chromosome 1s, one from our father and one from our mother. The single Chromosome 1 that we received from our mother was created by recombining the DNA from the pair of Chromosome 1s she received from her parents. The recombined Chromosome 1 might have been created by taking some DNA from the Chromosome 1 she got from her father, then crossing over to take the next portion of DNA from the Chromosome 1 she got from her mother, then crossing back over again in similar fashion. This process of recombination passes on only half of the DNA from each parent and might not pass on entire segments of DNA from some ancestors. Over the generations, many distant ancestors drop out of our genetic composition entirely.

How, then, do our lists of potential DNA relatives and our knowledge of direct ancestors from genealogical research correspond to each other?

• DNA segments shared with distant DNA relatives, when combined with knowledge of our family lines, can reveal or confirm common ancestors and break through brick walls.
• Many apparent DNA relatives who share only small segments of DNA with us are not in fact related to us.
• Known distant ancestors’ DNA might not have been passed down to us or to other testers who might in fact share those ancestors.
• Sometimes DNA testing indicates unknown branches in our family trees. Nevertheless, established family heritage is an important part of who we are. DNA testing combined with traditional research can aid in finding our ancestry.

I encourage traditional genealogists to add DNA testing to their arsenal of research tools. Unless you are just interested in a direct lineage, DNA testing is likely to expand your family knowledge considerably. When you separate the wheat from the chaff, those DNA relatives can be good connections.