A cousin can be missing from your AncestryDNA list even when the family relationship is documented. You may not have inherited the same matching DNA, or the match may fall below Ancestry's reporting threshold.
Ancestry also adjusts smaller matches through a process called Timber. It reduces the contribution of DNA that commonly matches across a population. With endogamy, generations of marriage within one community, the reduction can be substantial.
There are two different totals
cM, short for centimorgans, measures the length of matching DNA. Unweighted shared DNA is Ancestry's total before Timber. The match list's Shared DNA amount is the adjusted figure used to estimate your relationship.
On average, for Ashkenazi matches studied with totals below about 90 cM before Timber.
The reduction varied widely. Ancestry's white paper says Timber applies below 90 cM before adjustment; displayed values are rounded.
What it means for you: a match shown at 30 cM may have an unweighted total of 60 cM or more. Neither number tells you which ancestor the DNA came from.
A useful match can be far down the list
Sorting by Shared DNA sorts by the adjusted figure. One match in the saved analysis illustrates how far apart the two totals can be:
A saved example, with both bars on the same scale.
It appeared thousands of places down the saved list. The current position can change as new matches arrive.
What it means for you: search for a known relative by name. Do not assume that their position in the list tells you how close the documented relationship is.
A missing match does not undo the family tree
In one parent-and-child comparison, about a quarter of documented cousin relationships represented on the parents' lists had no match on the child's list.
Documented cousin relationships in the study's comparison with both tested parents. Twenty dots show the rounded proportion.
This counts family relationships represented in the comparison, not all matches or all families.
A child inherits half of each parent's DNA, but not half of every match. In the lists studied, no adjusted score was below 8 cM. An inherited match can therefore still be too small to appear after adjustment.
What it means for you: absence does not disprove a distant relationship. It also does not tell you whether inheritance, detection or Timber caused that particular absence.
What to check next
- Open the DNA details. Look for Unweighted shared DNA and Longest segment, the single longest continuous matching piece.
- Check a tested parent or older relative. They may have a useful match you did not inherit.
- Use the longest segment to find promising Ashkenazi leads. Then assess the unweighted total, records and known relatives together.
- Treat missing shared matches cautiously. That feature has its own visibility rules. A missing link is not proof of no relationship.
- Consider a second database. A compatible Ancestry raw file can be transferred to FamilyTreeDNA for free. Different testers and matching rules give another view, with endogamy still present.