|Related or not, my parents are married|
They explain it like this:
Since you inherit half of your DNA from each of your parents, it stands to reason that large blocks of SNPs where both alleles are the same would be an indication that your parents each inherited that block from the same ancestor. These are called 'Runs of Homozygosity' (ROH). There are other utilities available that look for ROH for other purposes, but this analysis is specifically aimed at determining how closely related your parents might be.They don't say so, but it is obvious if you think about it that the results are nothing more than an indication. After all, what they work with is your own personal DNA and since your siblings' DNA is different from yours, they will produce different results.
That's 23 cM altogether.
There are six of us, so you might think that we encompass all of our parents' DNA. We probably do, but we don't necessarily have their matching segments together.
GEDmatch offers another option - one that I have written about before in other contexts, as recently as last week. It's an idea I had during the Shavuot holiday, Tuesday night.
I created a simple Lazarus kit for my father. His six children are in Group 1 and his sister and brother are in Group 2. I could have added other family members, but any of those would have introduced DNA from other sources. My father's cousin Herb, for instance, would have brought DNA from his father who in theory could be related to my mother.
This Lazarus kit is 3490.2 cM.
For my mother, I used the same Group 1, her six children, but she has no living siblings for Group 2. So here I had to use my mother's sister's daughter and her brother's son. Not quite as good and with a chance of some contamination - at least from the nephew. The niece's father converted to Judaism and would have had no DNA in common with my father.
My mother's Lazarus kit is 2823.2 cM.
I ran a "One-to-one" between my parents Lazarus kits. THAT should give me a minimum for how closely they are related. Spoiler alert, it's more than the 23 cM than we saw in our "Are Your Parents Related" runs.
Nine matching segments for a total of 95.7 cM. That's four times 23 cM. Blaine Bettinger's Shared cM Project would define that as third cousins or second cousins twice removed. My parents are certainly not related that closely. Two of those segments - on Chromosome 10 - are adjacent and they alone are nearly 23 cM.
My parents' Lazarus kits show no match on the X.
But the biggest surprise is that there is nothing on Chromosome 3 or Chromosome 9 that Sarajoy and I show. And there are two segments on Chromosome 1 but neither is the segment that Amy and Judith show. I am guessing that the Lazarus algorithm is not designed to recognize those Runs of Homozygosity and that my cousins do not have those matches with my mother.
I don't have much practical use for "Are Your Parents Related," so the discrepancy really doesn't matter to me. But it certainly is one of those things that make you go "Hmmm."
I am posting this Sunday morning my time. This evening, I'll be speking for “Shorashim BaGalil” in Kiryat Tivon at the Library and Memorial Center Migdal Street 2. It will be the Hebrew version of
Lessons in Jewish DNA – One Man’s Successes and What He Learned On the Journey
I'll be speaking on the same topic on 19 June at 6:30, for IGS Rishon Lezion, Museum of Rishon Lezion, Ahad Ha’am 2.