What's becoming increasingly clear is even though we call identical twins identical, and we think of their genetic material as being identical, we need to be reminded that there are environmental influences that may change, actually, the characteristics of identical twins, reminding us, as we already know, that even though identical twins come from the same genetic material, in characteristics they may actually have differences as well.
Donna Krasnewich, M. Featured Content. Introduction to Genomics. This effect increases as the identical twins get older, because they are exposed to more and more diverse environmental events different illnesses, jobs, friends, habits etc. Silencing of one X-chromosome is also responsible for differences in female identicals. This silencing can happen AFTER the identical twins have been created and are developing when the embryo has grown to about cells.
Parents of twins have routinely been told that if their twins were born with the one placenta that they were identical however in recent years there have been a few reports of twins who were told they were identical for precisely this reason - only to later find out that they are in fact non-identical. This is due to something called 'chimerism' - when an individual is composed of 2 genetically different types of cells. A report has just been published which highlights a case study of chimaeric twins.
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Home Twins and families Frequently asked questions Twin facts Do identical twins always look alike? Do identical twins always look alike? Become a member. Join a study. However, the case may not be as inexplicable as it first appears. Leanne had suffered many similar fits in the past, and the rest of her family including her sister had been warned to keep a watchful eye on her. Knowing that Leanne had a tendency to have seizures that could render her unconscious — and knowing that being alone in water such as a bathtub or pool could be dangerous for her — it's not surprising that Gemma might have become concerned when after a few minutes she heard no activity such as splashing water from the upstairs bathroom where Leanne was bathing alone.
No "twin telepathy" is needed to explain this event; it's likely that any other non-twin member of the family who was home at the time would have reacted the same way. Such stories of twin telepathy or coincidences that make the news and are discussed in the context of some unexplained phenomena are, of course, the most dramatic ones.
Mundane coincidences that everyone experiences aren't newsworthy, and if Leanne's mother and not her twin sister had saved her it's unlikely we would have heard about it. By one estimate there are about million twins worldwide, and the fact is that most twins do not report experiencing any sort of mysterious telepathic connection.
If some special, psychic connection between twins is as strong and common as often claimed, then by chance alone we should expect millions of these amazing stories, not just a few dozen. As intriguing as the idea is, there is no credible scientific evidence that psychic powers exist, either in the general population or among twins specifically. Benjamin Radford, M. Live Science. Even as toddlers, they both showed the same aggressive streak. As they grew older, Lily seemed to be the artistic one, Gillian the athlete, spurred on perhaps by the Shaw's other children, Heather and Eric, who were both into sports.
The push and pull between genetics and family life is never far from their minds, the couples say. But then in the middle of a conversation Lily will roll her eyes exactly the way Gillian does, and Allyson is suddenly reminded of her daughter's twin.
That Lily and Gillian seem so similar, despite being raised in different families, underscores the genetic heritage that identical twins share.
But for two brothers in Maryland, the situation is just the reverse. Despite being raised in the same family, these identical twins couldn't seem more different. What could be so powerful that it trumps the combined effects of nature and nurture? Then it broke up into a nimbostratus. A bright-eyed six-year-old with glasses, Sam sounds like a professor in a meteorology class. Clouds are his latest passion, his mother says.
Before that it was trains, space, and maps. Lately, he's been working his way through a child's encyclopedia, gathering facts like a squirrel hoarding nuts, as she puts it.
The twins are both in first grade, but they attend different elementary schools, so that John can get the attention he needs. The boys' parents requested that we not publish their last name. When John's bus drops him off at home, he races inside, and Sam ambushes him with an affectionate hug. John laughs but doesn't speak. When Sam releases him, John walks to a box with stuffed animals and starts flapping his hands in excitement.
He's back in his own world. Sam has challenges too, mainly with social skills. The fact that they share a developmental disorder is not unusual. When one identical twin is diagnosed with autism, studies have shown, there's about a 70 percent chance the other will be too.
No one knows what causes the disorder, which is diagnosed in about one of every hundred children. Inheritance is thought to play a significant role, though experts believe autism may be triggered by as yet unidentified environmental factors. A study of twins in California last year suggested that experiences in the womb and first year of life can have a major impact. John's parents wonder if that was the case with him. Born with a congenital heart defect, he underwent surgery at three and a half months, then was given powerful drugs to battle an infection.
Shortly after Sam and John were diagnosed, their parents enrolled them in a study at the Kennedy Krieger Institute in Baltimore. Blood samples from the boys were shared with a team at nearby Johns Hopkins University looking into the connection between autism and epigenetic processes—chemical reactions tied to neither nature nor nurture but representing what researchers have called a "third component.
If you think of our DNA as an immense piano keyboard and our genes as keys—each key symbolizing a segment of DNA responsible for a particular note, or trait, and all the keys combining to make us who we are—then epigenetic processes determine when and how each key can be struck, changing the tune being played.
One way the study of epigenetics is revolutionizing our understanding of biology is by revealing a mechanism by which the environment directly impacts genes.
Studies of animals, for example, have shown that when a rat experiences stress during pregnancy, it can cause epigenetic changes in a fetus that lead to behavioral problems as the rodent grows up. Still other epigenetic processes are normal, such as those that guide embryonic cells as they become heart, brain, or liver cells, for example. Feinberg's study focuses on a particular epigenetic process called DNA methylation, which is known to make the expression of genes weaker or stronger.
To better understand how it relates to autism, Feinberg and his team are using scanners and computers to search samples of DNA from autistic twins for epigenetic "tags," places along the genome where methylation changes the pattern of gene expression. The goal of the study, still in progress, is to determine whether individuals with severe autism like John have different methylation profiles than other people. If they do, that might explain how he could turn out so different from Sam. Despite sharing the same keyboard, their bodies are playing different tunes.
It's a promising new approach, says Arturas Petronis, who heads the epigenetics lab at Toronto's Centre for Addiction and Mental Health. Researchers have known for some time that complex disorders such as autism are highly heritable.
But intensive scrutiny of DNA sequences themselves hasn't revealed why twins like Sam and John diverge so much in their behavior. The rest is still a mystery. As Feinberg and Petronis readily admit, such research is still at an early stage. The good news is that some of these processes, unlike our DNA sequences, can be altered. Genes muted by methylation, for example, sometimes can be switched back on again relatively easily.
And though it may not happen soon, the hope is that someday epigenetic mistakes will be as simple to repair as a piano that's out of tune. Back at the Twins Days Festival, Danielle Reed is standing in front of the Monell Center's research booth with a clipboard, asking twins to participate in her alcohol study. She's doing a brisk business, signing up one pair after another.
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