Loving the conversation so far, guys XD Especially since my class specialty is biology and chemistry. 
I don't know about you all, but I think magicians have a gene or a set of genes, which can be classified as magical or simply responsible for their magic, and one of those genes ( or just the gene ) has to be "unlocked", in order for someone to have magical abilities. I favor two possibilities:
1. A child has to have two recessive "magical activator" genes, in order to have magical abilities.
2. A child has to have a despiralised ( aka active ) gene, in order to have magical abilities.
The first option allows genetics to play a good role in this, whilst the latter - genes and a bit of luck maybe.

Both of Skye's parents were magicians, so I'm safe either way =P

By the way, what season will it be when we begin? Autumn?