Casey Lee knows all about that. She and her identical twin sister are often mistaken for each other. Despite the outward match, Lee points out, “Our personalities are so different.” Now 27, Lee is an art teacher, while her sister is an accountant.
The Martin twins, as they were referred to growing up, attended Holy Cross Lutheran School and graduated from Concordia Lutheran High School. Lee loves to tell the story about an incident at graduation time. As the sisters stood by each other, it was the first time a fellow student realized they were twins.
“She just thought we were the same person who changed clothes a lot,” Lee says.
Identical twins occur when a single fertilized egg splits and forms two parts. Identical twins have the exact same DNA. Scientifically, they are called monozygotic (MZ) twins. It is a myth that their fingerprints are identical, according to information from the University of Wisconsin’s Twin Project.
Fraternal twins, called dizygotic (DZ) pairs, form when two separate eggs are fertilized. They are no closer genetically than siblings who are not twins
Because identical twins are genetically the same, they are ideal subjects for medical and psychosocial research. Fraternal twins are often included in studies on genetics. For example, if the premise is a disease is linked to genetic factors, but identical twins have no greater incidence of the disease than fraternal twins, the evidence is strong that the disease is not influenced by genetics.
Duke University Medical Center is studying Alzheimer’s disease and twins, comparing incidence and environmental factors in identical and fraternal twin pairs.
The Minnesota Center for Twin and Family Research is one of several U.S. centers exploring genetics vs. environment in personality development and other psychosocial characteristics. In one Minnesota twin study of female preteen fraternal and identical twin pairs, genetics was found to have just a 30 percent influence on girls’ self-concept.
Yet studies on identical twins separated at birth reveal the significant role genetics plays in one’s outlook on life, in body mannerisms and even preferences for certain foods, colors or hairstyles.
Think you are seeing more twins these days? You are correct. The U.S. twin birth rate has increased by a whopping 76 percent in the last three decades, according to a CDC report released early last year. The increase is in fraternal twins only.
Fertility treatments are cited as the No. 1 reason. A surprising factor is the increased trend for women having babies in their late 30s and 40s, even into their 50s. As women get older, they produce more follicular stimulating hormone, or FSH. That translates into more eggs released at the same time by the ovaries, producing more fraternal twins.
Worldwide, the rate of fraternal twins is 22.8 born for every 1,000 births. But for identical twins such as Lee and her sister, the rate is just four per every 1,000 births.
When you look alike, “People are kind of fascinated,” Lee says, adding they can also be confused. Lee’s twin ate lunch one day at a Pizza Hut. Unaware her sister had been there, Lee went to the same restaurant an hour later.
“The waitress kept staring and giving me the strangest looks, acting weird,” she said.
Lee ordered her pizza, but this wasn’t a run-of-the-mill pizza. The sisters are allergic to dairy products, so they always order a pizza without cheese. Lee ordered a half-pepperoni, half-taco on thin crust, with no cheese.
“She acted like I was insane,” Lee says, but the server took the order and didn’t say a thing.
After Lee left, she called her sister to tell her about the very odd encounter at Pizza Hut. Her sister asked which Pizza Hut. That explained everything for the sisters. That waitress is still stymied.
This column is the personal opinion of the writer and does not necessarily reflect the views or opinion of The News-Sentinel.
Twins mythDo twin births in families “skip a generation?”
A woman whose mother had fraternal twins has a greater chance of bearing fraternal twins because the genetic trait for twinning is only in women. The man whose mother had twins has no greater chance of fathering twins than anyone else — but he can pass the trait on to a daughter, which is why some people erroneously think twinning “skips a generation.”
Source: National Organization of Mothers of Twins, www.nomotc.org.