Questions #2: 5 of us share a common ancestor, but only one 2cM marker

[georgemck]

As before, I have just begun using Family Finder. Right away I found 5 people with good overall matches and can show with genealogical research that we share the same great-great-great-great-grandfather (James Cadle of North Carolina). When I run a chromosome analysis, however, there is only one small, 2 cM, place where the 5 of us share a common region. 3 of these people share a common great-great grandfather on this line with me (Thomas Cadle, grandson of James) and these also only have this same 2cM region in common.

What’s happening here?

[LynCra]

Here is an overview of how much autosomal DNA you share with various relatives. http://www.isogg.org/wiki/Autosomal_DNA_statistics

The % each of you have inherited from the common ancestor may be different segments and so will not show as overlapping on the chromosome browser.

[Jim Barrett]

As indicated by the link above you are pushing the limit of FF with 5th cousins. I match a 4th cousin and not his full sister. I have several 5th-6th cousins who have tested and we see very little matching.

[LynCra]

I have a 4th cousin who does not match me, but matches my aunt who is his 3rd cousin once removed, so this shows that just one generation can make a difference.

[Haggis]

Or, taken to an even closer relationship, according to FTDNA I don't match a 3rd cousin, nor does my sister or the daughter of another sister. My sister, niece and I are all strong matches for a different 3rd cousin.

Those two 3rd cousins are 2nd cousins of each other and show an very strong match. The segments that we share with one 3rd cousin are entirely different than the segments she shares with the other 3rd (her 2nd) cousin. It's all the luck of the draw!