all traits are controlled by one gene with two sets of alleles

Answer 1

I'm assuming this is a T/F question. Alas, it's a bit of a trick question. Generally "All genes first used as examples when we are introducing students to Genetics" are of this type... and "All genes chosen and reported by Mendel" were as well... but in nature, virtually no process arises from action of a single gene product, so many genes will contribute to its outcome. Further, since different alleles need be different only by a single mutation and we've been evolving for billions of years, there will inevitably be dozens/hundreds/thousands of different alleles, though many will have indistinguishable phenotypes.

Example: consider human height. Would you say there is a 'tall' allele and a 'short' allele, and everyone is exactly one of the two corresponding heights? Or skin color--how many different skin colors would you say there are? Clearly, more than one gene/two alleles!