The shoe chromosome

Where do they get it from?
Are little girls born with the shoe chromosome?
Is it genetically programmed?
Mimi loves her first pair of wellies. She truly adores them.
And so she should. My heart skipped a beat or two when I finally got my wife to admit how much they cost.
But it does not matter that she will have outgrown them in 72 minutes from now, the next baby will be able to wear them. That's the beauty of it. They are unisex. Or so I've been told.
Anyway, for now they are worth every cent, for Mimi looks for them first thing in the morning and she would even wear them in her cot if she could.
I wonder at what the stage the handbag chromosome kicks in.
I can't wait!