Genealogical autosomal DNA evidence relies on segments of DNA shared between two or more individuals. When they are true matching segments, they provide information about shared ancestry. One problem that genealogists are currently facing is the inability to decipher between “real” or “true” matching segments and “false” segments.

I won’t get too much into all the different terminology of “real” versus “false” here, because it isn’t important and takes away from the more important discussion. Genealogists, like patent attorneys, can be their own lexicographer, just so long as they are understood by the reader by providing a good definition. So here are my definitions for this post (and I typically use these elsewhere): ... Click to read more!

We know that small segments shared between two individuals can be problematic (see Small Matching Segments – Friend or Foe?), whether the two individuals are closely related or distantly related (or not related at all, as we’ll see). I call small segments (which I usually classify as 5 cM or less) as POISON because it is currently impossible to decipher between which are real segments and which are not.

In the following analysis, I use the wonderful new Match-O-Match tool at DNAGedcom to compare my and my parents’ match lists from AncestryDNA. The Match-O-Match tool is a powerful spreadsheet analysis tool developed by Don Worth. It is available to DNAGedcom subscribers as part of the DNAGedcom Client. For more, see page 10 of the PDF HERE. Thank you Don for this great new tool! ... Click to read more!

When does DNA prove a relationship? When is a triangulation group sufficiently large enough to prove descent from an ancestral couple? When is a shared DNA segment large enough to prove someone is your first (or second/third/fourth, etc.) cousin? At what point does the DNA prove that I am descended from Samuel Snell? When does the DNA prove that you’ve found your great-grandmother’s biological parents?

NEVER.

And this is, perhaps, one of the greatest misconceptions in the post-DNA era of genealogy.

What is Proof?

Genealogy is the study of lives and relationships. Accordingly, genealogists spend much of their time identifying, hypothesizing, supporting, and sometimes rejecting, relationships.

Unless you have direct knowledge of a relationship (and even sometimes when you do), you identify relationships using evidence that you’ve gathered from multiple different sources (including DNA, census, land, tax, vital, and many other types of records). ... Click to read more!

Five-Part Series on Visual Phasing:

• Part I – Explaining visual phasing and identifying/labeling recombination points (November 21, 2016)
• Part II – Assigning segments of DNA (November 22, 2016)
• Part III – Using cousin matches to identify which grandparent provided the segments (November 25, 2016)
• Part IV – Mapping my own chromosome using the visually phased paternal chromosomes (November 26, 2016)
• Part V – Using the mapped DNA with new matches (November 27, 2016)

In “Visual Phasing: An Example (Part 1),” we identified and labeled all of the recombination points in the three siblings, Susan, Brooke, and Felix. Then, in Part 2 of the series, we used the identified and labeled recombination points to assign segments of DNA to the four grandparents (the blue grandparent and grey grandparent pair, and the purple grandparent and green grandparent pair). In Part 3 of the series, we used cousin matching to identify the grandparental source of the chromosomal segments. And finally, in Part 4 of the series, we characterized my paternal chromosome.

After Part 3, we had the following for Brooke, Susan, and Felix:

Now that we have this information, let’s see if we can use that to explore new matches with Brooke, Susan, and Felix. ... Click to read more!

Have you experienced this? You’ve identified a very clear cluster that includes numerous DNA matches that all descend from a single family, but you have no idea how this family links into your family tree. Try as you might, and despite building numerous trees, you can’t seem to figure out how these DNA matches and this single ancestral family link into your family tree. If this sounds familiar, you have an Unlinked Family Cluster!

Defining “Unlinked Family Cluster”

An Unlinked Family Cluster is a very specific phenomenon in genetic genealogy, one that is becoming increasingly common. We see more and more of these clusters for various reasons; the matching databases get larger and larger meaning that these clusters get larger and easier to identify. Additionally, the more we work with our closest DNA matches, the more we have very promising “left behind” matches that don’t fit into our known ancestry. Often, these “left behind” matches form a shared match cluster or a triangulated cluster around a specific family. This is an Unlinked Family Cluster. ... Click to read more!

This post was inspired by an excellent post from Lara Diamond today entitled “Long Segment–But No Close Connection“.

What is DNA Segment Frequency?

In addition to segment size, segment frequency may be another important consideration for genealogists.

There are two ways to think about segment frequency: The first measurement of segment frequency is the frequency of a DNA segment among all humans. This is a number that is currently unknown, and can’t yet reliably be estimated even with simulations; there just aren’t enough people in the world who have tested yet. This is especially true for a segment that might be found outside of people with European descent as testing of these populations has been minimal or practically non-existent. ... Click to read more!