"Twin suspects spark unique DNA test: Lab will try to tell which guilty of rape" is the headline to this story today in USA Today. Some quotes:
A private lab in Dallas is set to try something never before attempted by scientists who investigate crimes: separate the DNA of identical twins to try to show which member of the pair committed a crime.Also of interest is this story today from the Alameda Times-Star about twins.Unlike other people, [identical] twins begin life with the same genetic profile because they are formed when a single fertilized egg divides. But tiny mutations are known to occur in DNA, the cellular acid that carries the genetic code, as cells divide during an embryo's growth.
The lab, Orchid Cellmark, hopes to identify those differences to distinguish between the DNA of a pair of twins from Grand Rapids, Mich. The DNA of both men matches a semen sample from a November 1999 rape that was committed by one man.
The experiment is being watched closely by authorities across the nation. They say that in several cases, genetic evidence left at crime scenes — typically blood or semen — has linked identical twins to crimes that only one could have committed. The DNA testing used by law enforcement authorities and the FBI's national DNA database of convicted felons does not detect differences between identical twins. * * *
If differences are found in the Cooper brothers' DNA, they'll be compared with DNA from the rape. Even if a match is made, specialists say it could be difficult to get a court to accept the results of the new test.
“This is very cutting-edge stuff, (and) there has to be a first time for everything,” says David Lazer, a professor at Harvard University's Kennedy School of Government and a student of DNA evidence and public policy. “But you worry about a technology if it's only been done a handful of times.”
Marie Rogers of Daly City fits the demographics. She had Amy and Marissa, 10, when she was 41.And speaking of the Hamm twins, Slate had two interesting articles on these Olympic twins last month. This story, from August 18th, is headlined "Are Paul and Morgan Hamm identical or fraternal twins?" A quote:The girls are monozygotic, the new preferred term for "identical." It simply means that they came from one (mono-) egg (zygote). Likewise, the twins formerly known as "fraternal" are now called dizygotic.
About 70 percent of twin births are dizygotic twins. While they shared a womb, they are not any more genetically similar than any other siblings.
One reason for the change in nomenclature has to do with the fact that identical doesn't actually mean identical.
"Identicals kind of a misleading term," Rogers says. "My girls do look different. To me, they look different. But people say, 'I can't tell them apart.' One's heavier, one's a little taller."
Malmstrom says those from non-twin families tend to get confused about what it means to be identical twins.
"Identical means they have the same DNA, the same inheritance, the same biology, but it doesn't mean they're the same person," Malmstrom says.
Even in twin families, she says she's frequently encountered parents who say their twins can't be identical because they can tell them apart -- which is not really an accurate test. (Paul and Morgan Hamm claim to be dizygotic, but to most people they look exactly the same. Don't rely on the media to tell you, either. Various news services have called them fraternal and identical. Their parents say it doesn't really matter.)
Usually twins who share a placenta are identical, but the only way to really know is DNA testing.
Twin experts say the only way to know for certain whether twins of the same gender are identical or fraternal—or, to use the preferred scientific terms, monozygotic or dizygotic—is to conduct a DNA test. At this point, it's unclear whether the Hamm twins have had such a DNA test. An interview with Morgan and Paul's parents will hopefully provide some clarification. Another update to follow shortly.This follow-up August 19th article is titled "Are Paul and Morgan Hamm identical twins? Their parents say no. Science says yes." Some quotes:
So, Mr. Hamm, are your sons identical or fraternal? "Their parents do not believe that they're identical," he says.My opinion (for what it is worth, and this certainly is not law related) is that the Hamm father's statement that "The circle of hair on the top of each boy's head goes in opposite directions" indictates they are identical and, in fact, are what is known as "mirror-image twins."Mr. Hamm then lists the brothers' physical differences: The circle of hair on the top of each boy's head goes in opposite directions, their teeth are different, their noses are different.
But these are just the observations of a parent who has spent more than 20 years staring at his children. Have they taken a DNA test to confirm that they are fraternal? "We've never had them genetically tested," Mr. Hamm reports. * * *
The parents say fraternal. Paul and Morgan themselves say, according to AP reporter Nancy Armour and USA Gymnastics spokesman Brian Eaton, that they are fraternal. But medical science says identical. Slate sides with science, and hereby declares that American gymnasts Paul and Morgan Hamm are identical twins.
But using DNA to determine whether or not twins ARE identical is simple, as opposed to the USA Today story that began this entry -- using DNA to differentiate between identical twin.
Posted by Marcia Oddi at September 3, 2004 07:57 AM