shrinking shared cM

[stennor]

Thank you, Mr. McCoy. I asked FTDNA and learned that they did adjust their algorithm on July 1, 2021. (I don't recall them making any sort of announcement.) I haven't sifted through all of my notes, but it appears that the change had little or no effect on close relatives (first and second cousins),...

[stennor]

Does anyone know anything about FTDNA revising the Family Finder algorithm and so sharply reducing the shared cM for many of my matches? This seems to have happened sometime in the past year, perhaps even more recently than that.

[stennor]

Does anyone know of a way to estimate the DNA shared between first cousins when more than two people are involved?

I know that the average shared between any two first cousins is one-eighth of the total, or 12.5%. My sister and I have three first cousins, the children of our father's sister...

[stennor]

I sent a complaint to the FTDNA help desk and gave them the timings for loading from all nine of the accounts I manage. Here's their reply: "Thanks for the reply. We appreciate your feedback. I have passed along your comments and suggestions about the website to our team of Product Managers to...

[stennor]

I'm having the same problem. Does anyone know how to persuade FTDNA to remove the "improvements"?

[stennor]

I lose track of your explanation in the following places, with my questions in red....

[stennor]

Does anyone have any information about the accuracy of 23andMe versus Family Finder?

I have a Family Finder match whose longest shared chromosome segment is on chromosome #15, 10.57 cM ranging from 21,487,876 to 25,774,171. The same person matches me at 23andMe with a long segment also...

[stennor]

Mr. McCoy, thanks for your help. I thought you might be interested to know that I have nine matches who share the relevant segment of chromosome #15 with all four of the people in the Neuenfeldt family, the segments ranging from 33 to 47 cM (and matching me with 41 to 47 cM). The nine people match each...

[stennor]

Thank you, Mr. McCoy. The matches run from the very beginning of chromosome #15 out to end locations ranging from 33,415,482 to 36,220,253. I have no other matches (in either FTDNA or 23andMe) that cover that territory, and here's another wrinkle: I have another forty matches on chromosome #15, also...

[stennor]

Here's a question for everyone. In 23andMe, I have nine matches who share with me a segment of chromosome #15 starting at the very beginning and extending to a length of 41.23 to 43.39 cM (2048 to 2319 SNP). One pair shares 3% DNA, so they might be second cousins, but as for the rest, the 23andMe...

[stennor]

georgian1950, please fill me in on "the well-known pile-up areas," because that concept is new to me. My group ranges from 52,036,271 to 85,833,111.

[stennor]

I have four Family Finder matches who share with me closely overlapping blocks of 30-37 cM on chromosome #15. (Their total shared cM with me ranges from 52 to 82.) There's no discernible paper connection with me or with each other. Should I draw any conclusions?

[stennor]

I've taken the Big Y test, and one other man shares a confirmed haplogroup with me. Does this mean that we share a male line if we go back far enough? and a surname, if surnames were in use then?

[stennor]

Here are some numbers in case you don't already have them. On average, two second cousins share 212 cM. A second cousin, once removed or a half-second cousin would share half of that.

In my own family, there's a half-second cousin, and five of us are related to him in the same way, but...

[stennor]

One more detail I forgot to mention regarding my family of three siblings. Out of their total unduplicated matches, 53% appear in just one list or another. That is, each of the siblings has a number of matches that don't appear in the other two siblings' lists, and those unique matches add up to 53%...