Some DNA questions

[Tom Tom]

Hi,
I have never really understood DNA and the ethnicity indicators, but have used it before to make links with other people and confirm relationships. I do understand they change sometimes

I have a couple of questions about my Dad/Grandmother's DNA results.

Dad's ethnicity is:
68% England and North Western Europe
16% Scotland
10% Wales
4% Norway
2% Sweden


Grandma's ethnicity estimate is:
68% England and North Western Europe
15% Scottish
15% Irish
2% Nigeria (this was originally Benin and Togo but changed after an update).


My question is around the differences - as my Grandma doesn't have any Welsh, Norwegian or Swedish DNA, I can assume they come from my Grandfather's side.

My Grandad didn't have any Welsh ancestry, but his GG Grandad was Irish, so my dad's ggg grandad was Irish, but there is no Irish DNA.

I think I read elsewhere that Irish/Welsh/Scottish DNA are all interchangeable - is this correct?

One other point that I find really interesting - the vast majority of my dad's matches are also matches with my grandma, meaning that there are very few people on my grandad's side who have their DNA on the system. I think the closest match that will be on there from Grandad's side is a fourth cousin to my dad.

And finally... the Nigerian DNA for my Grandma intrigues me. Her great grandmother was born in the Caribbean and as yet, I haven't been able to find out anything about her parents (other than that dad was in the army and I know mother's name). Do you think this is likely to be where the Nigerian DNA comes from and is a suggestion that her great grandmother was descended from slaves?

Thank you for looking!