Very self-explanatory. I'd present this figure first, then get more serious with the APOE example.

i didn't draw this so i'm not sure what the deal is with the pants

I think the figure is trying to show the SNP is not associated with bad taste in trousers

Isn't that figure showing mutation instead of SNP? I always thought SNP implies some allele frequencies like for "genetic polymorphism" http://en.wikipedia.org/wiki/Polymorphism_%28biology%29#Genetic_polymorphism

I agree with Jan, that it might be better if there was a group of people with G and another with C

and yes, it'd be nice if one group had a higher frequency of ugly "trousers".