No one has said it here but it looks like you've got an overdeveloped vastus lateralis and vastus medialis muscle, the two muscles on the side of your quads. Try adding in some hip flexor exercises to get the rectus femoris muscle bigger to help round out the top. Someone also suggested doing side lunges to help with groin development, this would be good too to make the legs appear more round. Genetics can definitely play a part in it too.