Part Two: MyHeritage DNA Theories of Family Relativity
Theories of Family Relativity is part two of a series of articles to help you navigate MyHeritage DNA matches and tools. Read part one here.
Genetic genealogy is founded on the observation that when two testers share DNA, they share common ancestry. In the case of autosomal DNA tests (like the one offered by MyHeritage), the ancestor who was the source of that shared DNA could be through any of the respective testers’ ancestral lines and could be any number of generations back in the past.
Generally, when two testers share a large amount of DNA across multiple segments, they share more recent ancestors.
Meanwhile, if two testers share a single small segment of DNA, their common ancestor may be very distant. While shared autosomal DNA points to a genealogical relationship and perhaps the approximate generational distance to the source of shared DNA, documentation of both individuals’ genealogy is necessary to identify the common ancestor. Many testers are unfamiliar with the identities of their more distant ancestors and may need to learn how to extend their family trees. The Theories of Family Relativity tool at MyHeritage can help in these cases.
MyHeritage DNA Theories of Family Relativity
Census records, vital records, and compiled family trees might be used to connect the small trees started by each tester through generations of unknown ancestry. If two testers attach small family trees for the first few generations of their ancestry to their DNA test results, MyHeritage will search their extensive databases of indexed records and compiled family trees for a genealogical path connecting the two testers.
For example, if one tester reports the identity of their grandmother, then MyHeritage might find mention of that grandmother in a census record linking her to her parents. In turn, her father and his brother might be mentioned in a family tree. If the other tester reports his grandfather’s identity, MyHeritage might recognize that grandfather as the same individual as the brother of the first tester’s great-grandfather.
While Theories of Family Relativity may find a proposed connection between two testers, this does not always mean that the proposed common ancestors are necessarily the source of the shared DNA between the two individuals. The shared DNA might still come from another ancestral line. Even so, Theories of Family Relativity provide clues for further evaluation. One way to evaluate a proposed relationship is to consider shared matches, and Auto Cluster reports.
MyHeritage AutoClusters Tool
When two testers share DNA, they sometimes share genetic cousins. Evaluation of lists of shared cousins between a tester and any given match can sometimes reveal the existence of clusters of genetic cousins. Together these clusters of matches form a network of genetic relationships between a tester’s matches.
Genetic networks comprise subjects, nodes (matches), edges (relationships), and clusters. The subject of a network is most often a tester; nodes in a network are the matches to a tester. Edges are the relationships between a tester’s matches. Together these relationships form clusters.
The MyHeritage AutoClusters tool, licensed by MyHeritage from GeneticAffairs creator Evert-Jan Bloom, is a form of genetic network. Matches of a test subject are listed along the matrix’s right side and in the same order along the top of the matrix. Dark-colored boxes represent the intersection of a row and column associated with a single match. Light-colored boxes represent genetic relationships between genetic cousins. Relationships of the same color are grouped together in clusters.
Genetic clusters are often composed of individuals who are either:
• Descendants of a shared ancestor or ancestral couple
• Descendants of a shared ancestral couple along with some collateral relatives of both the
husband and wife in that couple.
• Members of an endogamous community.
If one of the individuals in a genetic cluster has a theory of family relativity or a known shared ancestor with a tester, it is possible that other members of the same cluster are also related through the same ancestral line.
Though genetic cousins are grouped in clusters, not all members of a cluster will necessarily be genetic cousins to all other members of the same cluster. This might happen because two members of a cluster are both descended from a common ancestor but are distant enough relatives that they do not share DNA with each other.
Alternatively, they may share a small amount of DNA. Still, they may not share enough DNA to be considered a shared match (this threshold is automatically set by MyHeritage and is described below the AutoCluster chart).
In the AutoClusters report, slightly darker colored boxes represent the intersection of a row and column dedicated to a single genetic cousin. Slightly lighter colored boxes represent genetic relationships between a tester’s matches. Tan boxes are present when a match does not share DNA (or does not share enough DNA) with another member of the cluster. Gray boxes represent relationships between genetic cousins who are members of different clusters. Along the right hand side, MyHeritage describes each cluster. Clicking on these descriptions will identify all members of the cluster.
In other situations, they may not be relatives to each other at all but may be related to most other members of the group. For example, most members of the group may descend from a common ancestral couple. Still, one member might be a collateral relative of the male common ancestor, and another member of the group may be a collateral relative of the female common ancestor.
In other cases, members of a cluster may have genetic relationships with members of other clusters. This can happen when each cluster is composed of descendants of separate ancestral couples, but one match is related as a closer relative and is descended from both ancestral couples. In other cases, a match might have independent shared ancestry with one or more genetic cousins in another cluster.
Yet, in other situations, both clusters might comprise members of the same endogamous population.
In all cases, Theories of Family Relativity and AutoClusters might be utilized to identify genetic cousins likely related through specific ancestral lines. Members of known clusters might be used to explore more distant ancestry of the corresponding ancestral couple or couples. Mystery clusters composed of genetic cousins with no known relationship to a tester but with a documented relationship to each other represent opportunities for further exploration in genetic genealogy research. Those individuals may be related through the ancestors just beyond a researcher’s brick wall!