Do identical twins have identical DNA?

Answer 1

Yes, excepting any mutations that occur after the original zygote breaks apart.

Answer 2

Wow. Please listen to me, I actually know what I'm talking about. "no...duh!" is the most blatantly wrong answer I've ever seen on this website.

They're identical BECAUSE they have identical DNA. Differences in height, etc have to do with environmental factors -- meaning what happens to them once they're out of the womb, not the DNA itself. That's why young identical twins are almost impossible to tell apart, and older ones can sometimes be distinguished by their looks.

The way Identical twins form is that an egg, which has already been fertilized (known as a zygote), divides (splits in two, and each part has a complete set of the gentic information) before any differentiation happens. Then each part begins to form a separate baby. Since they share the original zygote, they each have the DNA from that zygote.

The people who are saying "no, they're just sibblings" are thinking of fraternal twins. These guys are genetically different, because they are formed when the mother has a double ovulation -- meaning that she releases two separate, genetically different eggs in the same menstrual cycle and they both get fertilized -- each by different sperm. Therefore, they are no closer genetically than if you were born at a different time from your sibbling.

I have given you a link to the wikipedia article about twins, and it makes the distinction clearer.

Answer 3

Yep, they do at the beginning. I know you've been told that every cell in your body has identical DNA but it's not quite true; there can be little mistakes and mutations in the copying and billiions of cells are copied during development, all starting from one fertilized egg. In the same way as your own cells all starting the same in DNA and getting small differences, twins' DNA is like that, but with only one cell division separating the two cells that begin the two twins, it's pretty likely that they each start out with the same DNA. Then individual cells of each twin can have accumulated these small differences due to mistakes in copying.

Answer 4

Yes ... duh! (The "duh!" is for Molly.)

Please read megan_of_the_swamp's reply ... she knows what she is talking about.

phd4jc's answer is also correct (and also says yes), but I have a question. If methylation is the process of changing the gene expression without changing the gene itself (the DNA sequence), then how would this change the genome of identical twins to be different? Is it possible that since the study you are mentioning gets the DNA from blood samples, (i.e. from blood cells), that the small group of core cells used in the bone marrow to generate new blood cells have been altered by processes other than methylation? (Specifically, random mutation.)

As far as I am concerned, the DNA of two identical twins is indeed identical, unless some random replication mutation occurs *immediately* after splitting of the original fertilized zygote into two zygotes so that the two new zygotes themselves are genetically different.

Or let's put it this way ... not all cells in your body have *exactly* the same DNA. Every cell is the product of millions of replication events since the moment you were conceived ... and every one of these replication events can produce small changes in the DNA (mutations). So the DNA in a new bone cell created in your collarbone, might have *slight* DNA differences from bone cells created from other bone cells that have been replicating all your life in your left ankle. For the most part, any differences in DNA are minor and inconsequential ... unless they develop into cancer, or unless the cell in question is a gamete (a sperm cell or an ovum) in which case that random mutation will get passed on to any resulting offspring. All of this applies to the cells in your identical twin's body too. A cell from your body and a cell from your twin's body may not be absolutely identical in DNA ... but they won't be any more different, on average, than any two randomly selected cells in your body.

Answer 5

In a word: Yes :-) Although, a fun fact is that while, you can't tell identical twins apart from a DNA test, you can by their fingerprints :-)

Answer 6

both of the twins must have DNA. The DNA can be obtained by taking a blood test.

Answer 7

Identical twins start out with identical DNA.

Why? Because they started out as one egg that was fertilized by one sperm to create one organism. However, early on that 1 organism and that bunch of cells split to make 2 organisms. (In the case of Siamese Twins, they did not separate completely)

HOWEVER,
we live in an environment replete with mutagens. ANd our DNA is constantly undergoing mutations (why is cancer usually in older people? because cancer is an accumulation fo many mutations, usually 7-9, and it takes time for these mutation to accumulate) So the longer the twins are alive, the more mutations they are exposed to and the LESS alike their DNA becomes.

I figured some people wont believe me, so I have attached one (of a plethora) of articles supporting what I said above. It can be read in it's entirety at http://www.eurekalert.org/pub_releases/2005-07/osu-itm070705.php

The researchers studied 40 pairs of twins recruited in Spain , Denmark and the United Kingdom ; 25 of the pairs were female. The youngest set of twins was 3, and the oldest pair was 74. All of the participants were asked to complete questionnaires about their health, eating habits, physical activity, history of prescription medication use and tobacco, alcohol and drug consumption.

The researchers also drew blood samples from each participant in order to analyze and compare similarities and differences in the epigenome.

Results from the blood tests – and from the questionnaires – showed that the youngest set of twins had the most identical genomes. But that wasn't true for the oldest pairs of twins. Genetically speaking, these twins were the least alike.

The process that alters gene expression and behavior without changing a gene's DNA sequence is called methylation. Plass, who is also part of the human cancer genetics program at Ohio State, studies methylation in both normal and cancer cells in hopes of better understanding how the process affects the beginning and progression of the disease.

"Methylation is important for normal cellular development," Plass said. "It can help protect the integrity of a DNA sequence. But certain changes in the regulation of DNA methylation could have fatal consequences for a cell or individual."

Identical twins are born with an identical set of genes. Studying genetic differences in twins may give Plass and his colleagues insight into how methylation is regulated.

"One would expect identical twins to develop and express genes at the same levels, but in fact this changes over time," Plass said. "We think that methylation plays a genome-wide role in these changes."

Scientists think that foods, exposure to chemicals, physical activity levels and aging may all contribute to methylation in cells. But they don't understand how changes in DNA methylation occur, or how the process is regulated.

The DNA analysis in this study showed that twins who had spent less of their lives together, or had greater differences in their health and medical histories, had the greatest amount of methylation.

The next step for Plass is to compare the findings of this study to what he sees in cancer cell cultures in his laboratory.

"Nearly every tumor, every human malignancy shows changes in DNA methylation that mess up gene expression," he said. "If we understand what regulates methylation patterns, then we may be able to develop better treatment options for cancer."

Answer 8

Yes they do

Answer 9

yes !!! does identical give you no clue?

Answer 10

yes that is why they are identical..