The twin rule of pathology states that any heritable disease will be more concordant (that is, more likely to be jointly present or absent) in identical twins than in non-identical twins and, in turn, will be more concordant in non-identical twins than in non-siblings.
However, the study, at the hospital's twin research unit, found that identical twins were more likely to have a similar number of moles than twins who are not identical.
Maybe Galton's classic twins study was invalid: perhaps you cannot look at the similarities between identical twins, and those between non-identical ones, and conclude that the difference must necessarily be due to genes.
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This is that identical twins may not be as identical as appears at first sight.
It was more common for identical twins to both have Alzheimer's compared to non-identical, and a statistical analysis of risk rates in the groups gave the researchers their estimate of how significant genetic factors are.
Patients who receive a bone marrow transplant from an identical twin relapse half the time, perhaps because the twins share nearly identical immune systems.
It even distinguished between identical twins--their genes are the same, but their irises aren't.
The developing embryo starts to split into identical twins within the first two weeks after conception.
And it is only a predisposition towards having non-identical twins that is passed down through families.
Within a pair of identical twins, either both, or neither, will find quinine hard to swallow.
One problem is that separated identical twins do not actually provide a perfect nature-versus-nurture template.
ECONOMIST: WHAT WE LEARN FROM TWINS: The mirror of your soul | The
Another American scientist, Robert Plomin, has been working with 25, 000 pairs of identical and non-identical twins in Sweden.
ECONOMIST: WHAT WE LEARN FROM TWINS: The mirror of your soul | The
Identical twins Chandra and Leigh Watson have developed a style of sweet, soulful indie-folk that does more than nod to alt-country influences.
The mother of the identical twins, Marcelina Orellana, says Edith is "psychologically ill".
Mr Plomin has also set up a study working with 10, 000 pairs of identical and non-identical twins in Britain.
Laura and Linda Seber, for example, are identical twins from Sheffield Village, Ohio.
Instead, identical twins are epigenetically closer to each other than the fraternal sort.
Mr Bouchard saw an article on a pair of reunited identical twins, and decided to make a study of them.
Mr Bouchard now has a register of 8, 000 pairs of twins, some identical, some not, some separated, most reared together.
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You always hear about how alike identical twins are, so I wanted to know how Mike was different from his brother.
Once the identical twins reached the age of 50, there was an increased similarity in the number of pairs of individual moles.
This means that behavioural traits with a large genetic component are more likely to be shared by identical twins than fraternal twins.
The researchers looked at how common it was for identical twins to both have Alzheimer's, or for only one to be affected.
Ally and Claudia are identical twins, and their harmonies are incredibly precise.
Rather than looking at the similarities between identical twins, as most of the research tends to do, Epitwin will look at the differences.
Each person's DNA -- the genetic code in a person's cells -- is unique, except in the case of identical twins, he noted.
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Some of it emerged from the first large-scale post-Burt study of separated identical twins, run by Thomas Bouchard, a professor at the University of Minnesota.
Identical twins result when a fertilized egg splits into two embryos.
Moreover, separated identical twins are rarely separated at the moment of birth, and some of them are then reunited before they come under the scientists' eye.
ECONOMIST: WHAT WE LEARN FROM TWINS: The mirror of your soul | The
Although identical twins tend to share whorls, loops and arches in their fingerprints because of their common heredity, the precise patterns of their prints are not the same.
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