First cousin with no DNA match

[GillMcA27]

Is it possible for a first cousin to have no DNA match with me, my brother and another 1st cousin of ours? This cousin was adopted as her mother was unmarried. Her mother subsequently married my father’s brother and moved to Nigeria where they had another child but sadly the mother died in childbirth. None of the family knew anything about the adopted girl until her younger brother was 18 when she contacted him, telling him she was his half sister. Some years later, when their maternal grandmother died, a friend of their father told them that they were full siblings. Fast forward 40 years or more and we have taken Ancestry DNA tests. My father, this cousin’s reputed father, and the other cousin’s father were all brothers and, although I, my brother and the other cousin share the expected amount of DNA, Ancestry shows no match for any of us with the adopted cousin. Is that possible? I have toyed with the idea of asking her brother to take a test but we would all be upset if she turned out to be no relation!

 

[peter]

All 1st cousins are DNA matches - see the coloured chart in the Masterclass. Even half 1st cousins are DNA matches, which eliminates the possibility that the reputed father was only a half-brother to your father.
It may well be possible to find out who the adopted child's father really was, but it certainly wasn't your uncle.

 

[GillMcA27]

Oh, thanks Peter, I did think that might be the case. It is such a shame though, she and I have such a lot in common! Well, I’m not going to tell anyone! Thanks again, Gill