Recently, I had the opportunity to compare 2 children’s autosomal DNA against both of their parents. Since children obtain 50% of their DNA from each parent (except for the X chromosome in males), it stands to reason that all valid autosomal matches to these children not only will, but must match one parent or the other. If not, then the match is not valid – in other words – it’s an identical match by chance.
If you remember, the definition of a match by chance, or IBC (identical by chance) is when someone matches a child but doesn’t match either parent.
This means that the DNA segments, or alleles, just happen to line up so that it reads as a match for the child, by zigzagging back and forth between the DNA of both parents, but it really isn’t a valid genealogical match.
You can read about how this works in my article, How Phasing Works and…
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