How can Mary-Kate and Ashley Olsen be fraternal?!

How can Mary-Kate and Ashley Olsen be fraternal?

They played the same part in Full House. They both played Michelle Tanner. I think they look alike. If Mary-Kate had blonde hair she would look exactly like Ashley....right???

HELP ME PLEASE.

PLEASE LIST SOURCE(S)!!!!!

Thanks.

Mary-Kate and Ashley may have looked very much alike to those watching 'Full House', but they are 'fraternal' twins. They may look alike, but there are characteristics that make them un-identical twins. Scientifically, they were two eggs fertilized by two separate sperm at the same time. NOT, one egg that separated into two, making them identical twins.

I went to high school with fraternal twins. Until you knew them well, and were around them all the time, you could not distinguish which was which.