I had a line of Dwarfs once, Mexicans.
Double factor Dwarfs were the true dwarfs, single factor were intermediate in size. It was a Dominant characteristic, if it was present it expressed itself. I just can't explain how it popped up out of nowhere. It did not increase yields, on the contrary. It took just as long for a Dwarf to reach 40cm as it took a sister who was not carrying the gene to reach 2 metres. Yields were proportional to size.
N.