Two years ago I sent off a sample of my DNA for testing. When I first received the results, I was unable to make any connection between my tree and the trees of people with whom I shared DNA.
I have made some progress since, however, speeded up by more testing: I persuaded my father to have his DNA analysed by Ancestry.com. His results are interesting and will be very useful to my family history research.
He, of course, is one generation closer than I am to the ancestors revealed by DNA matches. The difference in the numbers of matches, however, is greater than I expected.
My father has 219 matches estimated to be 4th cousins or closer. Estimates of how closely a person is related to someone is based on how much DNA they share. I have only 74 matches where I am estimated to be a 4th cousin or closer. I share 56 of these matches – 76% – with my father. (AncestryDNA provides a tool to filter matches shared with your father.)
I am not surprised that the great majority of my matches are on my paternal side, for my mother’s family is from Germany, where DNA testing in family history research is comparatively uncommon.
My father has 546 pages of matches on AncestryDNA. I have 305 pages. He shares DNA with about 27,275 people on the AncestryDNA database. I share DNA with about 15,225. Assuming that the overall ratio of paternal to maternal matches is proportionally similar to matches for 4th cousins and closer, about 11,500 of my matches are paternal. This means that my father has more than twice as many matches as I have with people who descend from the same forebears.
In the inheritance process segments of DNA are divided unevenly. Sometimes a complete segment is inherited; sometimes no part of the segment at all is passed on. (The genetic genealogist Roberta Estes explains the difference between how much of an ancestor’s DNA we could share and how much we do share in a blog post at https://dna-explained.com/2017/06/27/ancestral-dna-percentages-how-much-of-them-is-in-you/)
No matter how children’s segments of DNA are divided when they are inherited, their parents have larger and more complete segments, and as a result have more matches, of better quality.
AncestryDNA identifies people with whom you share DNA and whose family trees include the same forebears. It may be that you and your match have inherited the matching DNA from these forebears. AncestryDNA calls these shared ancestor hints. I have twelve shared ancestor hints on AncestryDNA. All these are paternal. One of these hints is with my father. Of the other 11, two are not in common with my father. The tree matches are paternal but my father is not shown as having the same DNA.
Looking more closely at these matches I have but my father does not, I see that I share with one of these matches 6.1 centimorgans of DNA across one segment and with the other match I share 6.3 centimorgans across one segment. For one cousin we share 6th great grandparents and are 5th cousins once removed. The other cousin we share 4th great grandparents and are 5th cousins. Sharing 6 centimorgans is a very small amount of shared DNA. A centimorgan is a unit used to express the distance between two gene loci on a chromosome and it measures how likely the segment is to recombine as it passes from parent to child. I higher number of shared centimorgans means greater confidence in the match.
It is possible that I share DNA on my mother’s side with these two cousins and have the same people as ancestors on my father’s side, but the more likely explanation is that the AncestryDNA algorithms may have truncated the segments: these are in fact paternal segments. Examining the data for these two matches through GedMatch, FTDNA or MyHeritage could help provide some answers. These other three sites provide better information on where a person and a probable match share DNA.
My father has 22 shared ancestor hints: one hint with me, 9 shared with me and 12 hints where he has DNA matches with cousins and I do not. There are 12 cousins who have researched their family tree to the extent that they and I have identified shared ancestors. They are shown to share DNA with my father but they do not share DNA with me.
One of these shared matches is a third cousin once removed on the Chauncy line (my 4th cousin). My father and this cousin share 20.8 centimorgans shared across 3 DNA segments. AncestryDNA suggests I have no shared DNA: this match disappeared in one generation.
I have corresponded with several of my father’s matches. The smallest match with a shared ancestor hint has 6.4 centimorgans across 1 segment. She and my father are 5th cousins once removed. She grew up in the village of Caithness, Scotland, where our mutual forebears lived. Her father still lives there. She has researched further back on that line, and I look forward to learning more about these of my forebears from her.
Unfortunately, very few of my father’s matches with hints have uploaded their DNA elsewhere, and this limits our ability to make new discoveries. Uploading the DNA data from ancestry.com to these other sites (GedMatch, MyHeritage, Family Tree DNA) is free and is not hard to do.
One of the nice things one can do with the information one gets from these other sites and not through ancestry.com, is you can attribute segments of your DNA to particular matches. For this attribution you need information about your shared ancestors and the numerical information provided by the testing company for each match so you can visualise it on your chromosomes. The application is called DNA Painter (https://dnapainter.com )
Despite the limited data provided by ancestry.com, there is still much more analysis for me to do within the AncestryDNA database.