Kim Perell says it was hard growing up with a twin sister. She encourages her twins to be individuals and not compare ...

What makes twins fraternal? Find out how much these siblings share from conception on, and how similar or different they might be.

But now, a new study has found that genetics determines how much babies cry. That means we may not have much control over it, no matter how much swinging and singing we try.

Fraternal (dizygotic) twins, who come from two separate eggs, can be hereditary, especially if the mother has a tendency to release more than one egg at a time. Identical twins usually occur randomly.

The author (not pictured) married an identical twin and had fraternal twins. Courtesy of the author I had an emergency C-section and gave birth to my twins early at 35 weeks.

So identical twins, if their breast cancer is due to an inherited predisposition in a mutation in one of these genes that's been identified, then they would be at significantly increased risk ...