TWINS SHED LIGHT ON MYTH OF CREATING 'IDENTICAL' PEOPLE
BY JoANNE YOUNG -- Lincoln Journal Star

    The fingerprints of identical twins Will and Robert Scott match almost perfectly.
    The same blood travels from scalp to toes of the 28-year-old men. Their teeth — complete with fillings — and eye color are indistinguishable.
    But Will is more forgetful than his brother. Robert more apt to be on time.
    Robert is finicky. Will is not. And while Will is a husband and father, Robert chooses bachelor life.
    "We look at things differently," said Will, "yet we have a lot of similar interests."
    For eons, nature has conducted its own cloning experiments. The results: identical twins, occasionally, identical triplets.
    Nature performs its science daily while the world simultaneously wrings its hands and watches in fascination as scientists unwrap — experiment by experiment — what will someday be the ability to clone humans.
    And if we would only pay attention, it also debunks the myths that science fiction and imaginations weave about human clones.
    "Odds are such that it is impossible to re-create a person, to clone a human being and get what you expect," said Dr. Michael Schmidt, a Lincoln pediatrician and clinical geneticist.

Will and Robert Scott

    Even with identical twins, who originate from the same egg and sperm combination and are usually raised in the same environment, differences develop. Once cells begin to divide in independent beings, anything can — and does — happen.
    Consider Lacey Jennings and Lisa Brinker, 30-year-old identical twins and stepsisters to Will and Robert Scott.
    The women live 1,800 miles apart, in Chicago and Scottsdale, Ariz. Both have blue eyes and blond hair. But Lacey is single, wears contact lenses and cuts her hair shorter. Lisa is married, expecting a baby, wears her hair longer and has never had her eyes checked. There's also a slight difference in height.
    And at a critical time in their development — the teen-age years — the two decided to maximize their differences by attending separate high schools.
    "We just needed some space," said Jennings. "Not only did we get to know twice as many people, we appreciated each other more."
    Separating is how identical twins start out.
    Sometime in the first seven or eight days after the mother's egg and father's sperm unite, as cell division begins and the conception tumbles through the fallopian tubes toward the uterus, the cell mass that might have been just a Lacey splits into a Lacey and a Lisa.     It's an accident of nature. And identical twins result about once in every 250 to 350 births.

Lisa Brinker

    But in fact, doctors speculate 10 percent to 15 percent of all pregnancies start out as twins. More times than not, one embryo fails to develop and is reabsorbed. Fraternal twins — which occur once in every 70 to 89 births — come from two separate fertilized eggs, and are no more alike than any siblings.     Identical twins are actually more alike than a clone created in a petri dish would be. And their differences debunk science fiction notions that an exact replica of a person or animal can be cloned.
    With a clone, part of that difference would be found in the donor egg's mitochondrial DNA, the genetic material contained in thousands of chromosomes that float in the egg's cellular matter. Cloning requires matching a donor cell, which contains most of the important genetic keys to who a person is, with a donor egg that has had its nucleus removed.

Lacey Jennings

    These mitochondria —there are about 100,000 in the egg compared to 100 in the sperm — are important to the whole body, regulating the energy processes in each cell. With that energy, muscles contract, nerves send messages, glands produce chemicals.
   Certain disorders can be passed to the child through the mitochondrial DNA. Alzheimer's disease, for example, may be brought about because of changes in mitochondrial DNA. Aging may also be a function of this DNA.
    The only way for a clone to get similar intelligence, strength, abilities and appearance — as with identical twins — would be to match the nuclear DNA with the mitochondrial DNA found in the egg of the cell donor's own mother, Schmidt said.
    For example, to get the most similar replica of, say, Michael Jordan, scientists would have to take a cell from Jordan and fuse it with an egg from Jordan's mother.
    "It's such an important influence," Schmidt said.
    Even with the same egg and nucleus, changes or mistakes can occur as cells divide in utero and after birth, Schmidt said. External influences — cigarette smoke, chemicals, medicines, radiation — can bring about changes in cells.
    "There are mechanisms that can repair DNA, but sometimes the repair isn't exactly the same," he said. "If you could completely sequence twins' DNA, you would find it is different — mostly in the noncritical parts of DNA."
    But if an important part is damaged and repaired wrong, he said, the mutation continues.
    "The system is really good, but it's not perfect."

Twin sisters, Lisa and Lacey

 
    Twins also have differences in intelligence and personality.
    Intelligence is a result of many factors, some not related to DNA. In 100 sets of identical twins, only 70 will have very similar IQs.
    With personality traits, the correlation is only 50 percent — half will have similar personalities, half will have personalities that are quite different.
    Take the famous conjoined twins of the 1800s, Chang and Eng. The two not only shared their genetic makeup, they had the same experiences all their lives since they were never separated. Yet they were said to have had completely different personalities.
    Chang, the dominant brother, had a temper and a quick intelligence. Eng was quieter and had wider interests. Chang was a drinker; Eng was not. Chang was harder for people to get along with, while Eng was well liked.
    The differences, however they come about, bring with them completely unique individuals.
    For Will and Robert Scott, those differences likely occurred in about the seventh day of conception. When their egg split — later than most — differentiation of the cells into what would be the head and trunk, the right and left sides, had likely begun.
    The result: mirror twins, each the reflection, the mirror image, of the other. One is right-handed, the other left-handed. Their hair whorls twirl in opposite directions.

Michael Schmidt, Lincoln physician

    About one-quarter of identicals are mirror twins. Sometimes even internal organs and skeletal features are on opposite sides of the body.
    Will and Robert say they have similar interests but approach things differently.
    "He has his strengths, I have my strengths," Robert said.
    As boys, the two were very competitive and frequently teased, wrestled and squabbled. As they have matured, they've stayed close but still compete and play pranks on each other.
    "We've always been each other's best friends," Will said. "I probably know him better than he knows himself — outside in and inside out."
    Robert met Will's wife, Tracy, while all three were in college. But when she came back to visit him, it was Will she encountered — and Will she stuck with.
    "I knew her personality would work much better with Will's," said Robert.
    They look less alike now than they did as kids, thanks to two broken noses for Robert but only one for Will, and seven minor head injuries for Robert, but only six for Will, the result of childhood and sports accidents. Will is also slightly taller and heavier than Robert.
    Today, both live in Lincoln. Both have college degrees in economics and finance and work in similar fields. Will works in commercial real estate for B&J Partnership. Robert manages family assets in a small investment company.
    Will and Robert Scott know they are distinctly different beings. And they believe no two people — cloned or otherwise — could be exact duplicates.
    "They say you are a bit of every person you have met," Will said. And there's no way, he said, a cloned person — a delayed twin — could meet every person his or her earlier twin met.
    Similarities and differences aside, Will and Robert say being twins is great fun.
    "I feel blessed, really blessed, always having him around," Will said.
    His brother echoed the thought. "I can't imagine not having him."
    Reach JoAnne Young at 473-7242 or jyoung@journalstar.com.  

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