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The Claim: Identical Twins Have Identical DNA (No, copy-number variation strikes again!)
NY Times ^ | March 11, 2008 | ANAHAD O’CONNOR

Posted on 03/15/2008 12:24:17 AM PDT by neverdem

Really?

THE FACTS

It is a basic tenet of human biology, taught in grade schools everywhere: Identical twins come from the same fertilized egg and, thus, share identical genetic profiles.

But according to new research, though identical twins share very similar genes, identical they are not. The discovery opens a new understanding of why two people who hail from the same embryo can differ in phenotype, as biologists refer to a person’s physical manifestation.

The new findings appear in the March issue of The American Journal of Human Genetics, in a study conducted by scientists at the University of Alabama at Birmingham and universities in Sweden and the Netherlands. The scientists examined the genes of 10 pairs of monozygotic, or identical, twins, including 9 pairs in which one twin showed signs of dementia or Parkinson’s disease and the other did not.

It has long been known that identical twins develop differences that result from environment. And in recent years, it has also been shown that some of their differences can spring from unique changes in what are known as epigenetic factors, the chemical markers that attach to genes and affect how they are expressed — in some cases by slowing or shutting the genes off, and in others by increasing their output.

These epigenetic changes — which accumulate over a lifetime and can arise from things like diet and tobacco smoke — have been implicated in the development of cancer and behavioral traits like fearfulness and confidence, among other things. Epigenetic markers vary widely from one person to another, but identical twins were still considered genetically identical because epigenetics influence only the expression of a gene and not the underlying sequence of the gene itself.

“When we started this study, people were expecting that only epigenetics would differ greatly between...,”

(Excerpt) Read more at nytimes.com ...


TOPICS: Culture/Society
KEYWORDS: cnv; copynumbervariation; copynumbervariations; dna; epigenetic; epigenetics; epigenome; epigenomics; genetics; genomics; health; identicaltwin; identicaltwins; monozygote; monozygotes; twin; twins
Phenotypically Concordant and Discordant Monozygotic Twins Display Different DNA Copy-Number-Variation Profiles
1 posted on 03/15/2008 12:24:19 AM PDT by neverdem
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To: neverdem

Sending to my identical twins...don’t ever try to play a game of chance against them. ;)


2 posted on 03/15/2008 12:54:18 AM PDT by sageb1 (This is the Final Crusade. There are only 2 sides. Pick one.)
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To: neverdem

Not surprised: twins have different fingerprints.


3 posted on 03/15/2008 3:20:28 AM PDT by Does so (...against all enemies, DOMESTIC and foreign...)
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To: neverdem

Epigenetics is going to be the next great field in medicine.


4 posted on 03/15/2008 3:27:44 AM PDT by Straight Vermonter (Posting from deep behind the Maple Curtain)
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To: neverdem

What the article says is the they DO have identical DNA, but that changes can develop soon after fertilization. Another case of the headline being written by an brain-deficient moron.


5 posted on 03/15/2008 3:31:49 AM PDT by Leftism is Mentally Deranged
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To: Leftism is Mentally Deranged

What happens, is every time the cells divide, there are changes occurring. In other words, the succeeding generation of cells is not quite identical to the original cell. It can certainly make for some interesting differences in characteristics of a set of monozygotic twins, while there are still a lot of similarities.


6 posted on 03/15/2008 3:38:54 AM PDT by punster
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To: twin1

Twin ping.


7 posted on 03/15/2008 4:59:37 AM PDT by twin2
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To: neverdem

Great information, neverdem. Thanks for posting this!!


8 posted on 03/15/2008 5:15:06 AM PDT by syriacus (The maNYical steamroller has trapped himself in a swamp of his own making.)
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To: Leftism is Mentally Deranged
Technically, the headline is accurate by your reasoning (that they *do* have identical DNA), stating that twins have identical DNA.

There is only a suggestion that this isn't the case (which is the case for some, and if all the cells in a twin are taken into account, not only the first one).

9 posted on 03/15/2008 5:37:12 AM PDT by Jedi Master Pikachu ( What is your take on Acts 15:20 (abstaining from blood) about eating meat? Could you freepmail?)
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To: neverdem
Image hosted by Photobucket.com i always thought twins were one egg and two sperm... that alone should be able to account for the difference.

or is that fraternal twins?

10 posted on 03/15/2008 5:59:33 AM PDT by Chode (American Hedonist ©®)
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To: Leftism is Mentally Deranged
Well their DNA is the same, but its MODIFICATION pattern is different! The DNA sequence is identical, but they end up getting methylated at different positions, which changes gene expression.

So their DNA is the same.....but different.

11 posted on 03/15/2008 6:03:32 AM PDT by allmendream ("A Lyger is pretty much my favorite animal."NapoleonD)
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To: Chode
Fraternal twins are two different eggs and two different sperms. AFAIK. One egg and two sperm couldn't make anything viable. One egg that split into two and then got fertilized by two different sperm might, but cellular replication is pretty well stopped in an egg cell until it is fertilized so I think it more likely that it would split after fertilization (resulting in identical twins).
12 posted on 03/15/2008 6:06:15 AM PDT by allmendream ("A Lyger is pretty much my favorite animal."NapoleonD)
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To: martin_fierro; blam
Ping!
13 posted on 03/15/2008 7:32:01 AM PDT by SunkenCiv (https://secure.freerepublic.com/donate/______________________Profile updated Saturday, March 1, 2008)
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To: wintertime

ping


14 posted on 03/15/2008 7:42:22 AM PDT by wintertime (Good ideas win! Why? Because people are not stupid.)
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To: allmendream
Image hosted by Photobucket.com thx... my Mom's twin was her Brother. 8^)
15 posted on 03/15/2008 7:48:08 AM PDT by Chode (American Hedonist ©®)
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To: mikrofon; Charles Henrickson
Psychic Soul Brothers ≠ Twins.
16 posted on 03/15/2008 7:51:38 AM PDT by martin_fierro (Sorry.)
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To: neverdem

“Monozygotic twin” sounds pretty cool...maybe that will replace the expression “identical twin.” Discordant monozygotic twins would be identical twins who fight a lot with each other.


17 posted on 03/15/2008 7:52:30 AM PDT by Verginius Rufus
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To: neverdem; SunkenCiv
I Am My Own Twin (part 1)
18 posted on 03/15/2008 7:53:48 AM PDT by martin_fierro (< |:)~)
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To: Leftism is Mentally Deranged

Good point. And they sure do change into different beings as they grow older and things happen to them.


19 posted on 03/15/2008 8:06:52 AM PDT by AmericanVictory (Should we be more like them, or they like us?)
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To: Leftism is Mentally Deranged
I followed the link to the NYTimes (something I hated to do). The last two paragraphs read:


THE BOTTOM LINE

Identical twins apparently do not have identical DNA.

20 posted on 03/15/2008 8:13:50 AM PDT by ChessExpert (Reagan dismantled the Russian communist empire of 21 conquered nations)
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To: sageb1

“A few years ago in Dunwich a half-witted girl bore illegitimate twins. One of them was almost human.

-—H. P. Lovecraft


21 posted on 03/15/2008 8:41:05 AM PDT by Mike Darancette (Democrat Happens!)
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To: allmendream; martin_fierro; Charles Henrickson
The DNA sequence is identical, but they end up getting methylated at different positions

Which brings up the thought that, if you think you see identical twins at a bar, you've probably had too much...

22 posted on 03/15/2008 10:00:57 AM PDT by mikrofon (Give me a Double)
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To: Straight Vermonter
Epigenetics is going to be the next great field in medicine.

Epigenetics is one thing. Copy number variation is quite another. It includes a range in the number of copies of a gene, from deletion, i.e. the absense of the gene altogether, to multiple copies of the same gene to different versions of a gene that makes a different, but functionally similar, protein, e.g. pancreatic amylase and salivary amylase. Click on the keywords copynumbervariation, copynumbervariations and cnv. It's not just simple Mendelian genetics and epigenetics.

23 posted on 03/15/2008 10:37:22 AM PDT by neverdem
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To: Leftism is Mentally Deranged
What the article says is the they DO have identical DNA, but that changes can develop soon after fertilization. Another case of the headline being written by an brain-deficient moron.

No, check the link in comment# 1 and the keywords copynumbervariation, copynumbervariations and cnv. In the case of twins, copy-number variation means that the twins can have zero to multiple copies of the same gene.

24 posted on 03/15/2008 10:54:48 AM PDT by neverdem
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To: El Gato; Ernest_at_the_Beach; Robert A. Cook, PE; lepton; LadyDoc; jb6; tiamat; PGalt; Dianna; ...
How epigenetics integrates nuclear functions

It's unrelated to the main theme underlying this thread, copy number variations, but since epigenetics was mentioned so often, I managed to come across this review article from a conference in 2005. It's fascinating, even if it may be already out of date.

25 posted on 03/15/2008 11:58:10 AM PDT by neverdem
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To: mikrofon
Unless they happen to be the O'Malley's
26 posted on 03/15/2008 2:23:39 PM PDT by mikrofon (Happy St. Paddy's Day)
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To: Does so

Not surprised: twins have different fingerprints.
....and fingerprints are not the result of genes?


27 posted on 04/09/2008 2:00:10 AM PDT by Bellflower (A Brand New Day Is Coming!)
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To: Bellflower
....and fingerprints are not the result of genes?

The article says, "identical, they are not". My recollection is that fingerprints aren't programmed like genes. They "just grow".

Monkeys have fingerprints, too, BTW. (And suspect they are not alike in monkey-twins as well—though I haven't checked!)

:)

28 posted on 04/09/2008 3:21:55 AM PDT by Does so (...against all enemies, DOMESTIC and foreign...)
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