When it comes to doubles, one of the first things that to comes to mind are twins! Seventy percent of twins are fraternal, while 30 percent are identical. But it's not always so easy to tell.
Identical twins, known as monozygotic*, develop from a single fertilized egg, or ovum. The egg splits into two genetically identical embryos that have identical genomes, are the same gender. Identical twins occur randomly but are more likely when the mother is older.
Non-identical, or fraternal, twins develop from two ova, or eggs, that are fertilized at the same time by two sperm. They have different genomes, can be male, female, or one of each, and are called di-zygotic*. Fraternal twins tend to run in families, as opposed to occurring randomly, and are as genetically similar to one another as they would be to any other sibling.
*Zygote: Once an egg is fertilized, it becomes a zygote. After two weeks of rapid cell division, the zygote becomes an embryo.
Twins Mandy and Marcie, both 35, are unsure whether they are identical or fraternal. "Growing up, we always told people that we were fraternal," Marcie says. "Then we started to get [people saying], 'No, you're identical,' so we just started saying, 'OK, we're identical.'"
The sisters take a DNA swab test to determine once and for all what type of twins they are!
Tricia, 30, hates her double chin. "Most often, a double chin is associated with somebody who's overweight," she says. "I'm not. I workout three to four days a week, and it just won't go away. Even when I was younger and thinner, I always had this problem."
With her wedding around the corner, Tricia wants to get rid of her double chin for good.
"Tricia has microgenia, which is a small chin," plastic surgeon Dr. Christine Petti says. "It's an anatomical deficiency in the bone of the jaw. This is a chronic problem. This is not something that just occurred with a weight change. This is genetic."
• More from Dr. Petti!
Shea's daughter, Annabelle, is reaching the toddler age where acting out becomes commonplace and frustration grows: the terrible twos!
"For the first two years, Annabelle was a happy, easy, sweet little girl," Shea says. "I didn't even know what a tantrum was."
Now, the fits occur frequently and Shea is at her wit's end.
• How did you deal with the terrible twos? Tell us here!
Are you at risk for double vision? Is being double-jointed bad for you? The Doctors tackle more double dilemmas.