So I'm in a thread at the moment that has briefly touched on the relative likelihood of muggleborn siblings having magic, and I was wondering whether any remembers if there's anything in the books about it? I know the Creevey brothers were Muggleborn, but are there any other examples and/or mentions?
I guess the antithesis of that is Lily/Petunia but I don't know whether it establishes which one of those is the unusual situation. All the other Muggleborns I can think of either don't mention siblings or are known to be only children.
I don't remember anyone seeming particularly surprised that both Creevy brothers had magic, but the books didn't really focus on them much so it's hard to say.
In Sonoraverse, Sully has a sister who's not magical, but Holly had one of three half-siblings come to join her at the school. Conner Pierce was the only one of his siblings to have magic. I can't recall off hand which other muggleborns did and did not have siblings.
I've written both and I'm fairly sure I've had both reactions... i.e. people being surprised that my Muggle-born's sibling was not magical, as well as people being surprised when they were. Pepper was one of 7 children and one of 2 with magic (seemed to be tied into whichever genes made them ginger in her family :-p). I am magical with a non-magical sister. Maybe it goes both ways often enough that neither is really surprising? That might be the easier thing to assume...
13Michael GrosvenorA bit of both199Michael Grosvenor05
According the Harry Potter Wiki...muggleborns are descended from squibs. The magic gene resurfaced after a few generations, so I don't think muggleborn siblings having magic would be rare.