I have alway been told that Fraternal Twins were a genetic thing (more than one egg released at a time), but as you get an X chromosome from your mother and father I don't think it is just inherited from your mother.
Also I understood that identical twins were not genetic and just a "fluke" occurrance that the egg splits.
Women do tend to produce more eggs after 35 so chances of having multiples after 35 go up :)
Is any one out there an expert?