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  2. chance of a longest segment being 106.5 cM for a second cousin

chance of a longest segment being 106.5 cM for a second cousin #dna

Herbert Lazerow
 

I cannot answer either of your questions; perhaps a professional
statistician could.
It seems to me that the 106.5 is more in the range of first
cousins. My two first cousins on MyHeritage and I share longest
segments of 82 and 115 cMs, but the total shared in both cases is
almost 900cMs. On Family Tree DNA, the same two first cousins measure
in slightly lower: 866/61 and 835/108. A third first cousin claims
1108/114.
As for second cousins on MyHeritage, they range >from 291/75 to
240/43 [259/40 on FamilyTreeDNA], to 200/21. Second cousins on
FamilyTreeDNA are at 259/40, 234/27 and 194/25.
I conclude that those six recombinations provide much room for
variation, but even granting that, I suspect that 106.5 cMs as a
longest shared segment is probably unusual for a second cousin. Of my
5 known second cousins who have tested, none are anywhere near 106.5
cMs.

Bert
--
Herbert Lazerow
lazer@sandiego.edu

My second cousin and I share a longest
segment of 106.5 cM's. His maternal grandmother and my paternal
grandmother were sisters, but this is not X-DNA. (The total number of
our shared cM's is 310.6)
If I understand correctly, there were six chances of recombination
between the great-grandparent generation and our generation. (If my
understanding is incorrect, I would very much appreciate it if someone
would enlighten me.)
What is the statistical likelihood of a run of 106cM's remaining
intact in 6 chances of recombination? It seems to me that it would be
rather low.
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