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Do twins have the same DNA?
Answer 1:

The answer to this question depends on what type of twins they are! There are two types of twins. In one case, twins can be produced when two eggs are present at the same time inside the mother, and both of these eggs get fertilized. Each of them eventually grows into a separate baby. Because each egg and each sperm started with different DNA, the babies that grow from each have different DNA. These twins are called fraternal twins, and they are just like other siblings, except that they were born at the same time! (This is why sometimes you might meet a brother and sister who say they are twins). In the other situation, there is only one egg, and it is fertilized by only one sperm. Normally the fertilized egg would divide and grow to form one baby. However, sometimes after the egg is fertilized and starts to divide, it can split apart. After it splits apart, each half can continue to divide and grow into a baby! So, in this case, the two babies came from one egg. These kinds of twins are called identical twins-- and yes, they do have identical DNA, because they came from the same fertilized egg! You can remember it this way: fraternal twins each have their own DNA, while identical twins share theirs.

Even though identical twins have the exact same DNA, though, they aren't really perfectly identical. That's why every mother can tell her identical twin babies apart. The reason they aren't identical is that each of them develops separately, and lives a separate life. For example, if one of them has an accident riding his bike, then he might injure himself and get a scar, while his twin brother does not have one. Also, some things in development are a little bit random, and not just due to DNA. For example, identical twins have similar, but not identical, fingerprints.

Answer 2:

Identical do have the same genotype. After all, they come from the same fertilized egg. Recent studies have shown that identical twins have very "similar" not "identical" DNA, but for the most part, according to basic biology it is identical. Identical twins aren't completely identical because DNA is essentially like instructions to building something, how your body decides to build that is random. This is why identical twins can have differing fingerprints. Another big factor why identical twins aren't necessarily completely identical is the environment which each of them were raised in. But for the most part, basic biology says identical twins share the same DNA. More research is being done to investigate this.



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University of California, Santa Barbara Materials Research Laboratory National Science Foundation
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