Zygosity Testing of Twins

Discussion in 'The First Year' started by ECUBitzy, Feb 19, 2013.

  1. ECUBitzy

    ECUBitzy Well-Known Member

    Twin DNA zygosity test

    Ever wondered what a twin DNA testing is? Well, essentially this is a DNA test that is aimed at telling you whether twins are identical or fraternal. While one might think the difference between identical twins and fraternal twins is always patently obvious, this is not always true. There are in fact times when it is rather hard to tell whether two twins are actually identical or fraternal.

    Monozygotic twins

    “Monozygotic twins” is actually the scientific terms used to refer to twins that are identical. This term explains the nature of fertilization which results in identical twins. The prefix mono simply means “one or single” while zygotic is an adjective which refers to a fertilized ovum. Monozygotic twins are the result of a single fertilized ovum which then splits into two. Following the split, two individual fetuses are formed. Given the fact they each fetus has been formed from the same egg, they also each has the exact same genetic blue print. This is what makes the identical and indistinguishable.

    Dizygotic twins, the scientific terms which refers to fraternal or non identical twins, result from a different fertilization process. If we analyze the derivation of the word, we have the prefix “di” which means “two” and once again the term “zygotic”, the adjective derived from the noun “zygote”, meaning a fertilized ovum. In this case, the term clearly tells us the fraternal twins result from two fertilized eggs. In other words, two individual sperm cells fertilize two separate ova forming two different fetuses. Because these fetuses are not formed from the same egg or the same sperm cell, they have different copies of genetic material and essentially the genetic makeup of fraternal twins is not any different to that of normal siblings. They share about 50% of their genes.

    Twin DNA testing

    Identical twins do usually look identical but sometimes fraternal twins are also very similar in appearance. Because of this, sometimes parents of twins or twins themselves wish to confirm whether their twins are identical or fraternal. But there may be other motives behind simple curiosity.
    For example, the fact the identical twins have the exact same genetic makeup means that they also share the same blood group. In case of a medical emergency where blood is required for one twin, the other twin makes a perfectly suitable donor.

    Moreover, identical twins who donate organs to each other have a far lower chance of the organ being rejected. There is no need for immunosuppression after for example a kidney transplant. Following many transplants, doctors need to suppress the immune system of the organ recipient using drugs. This is because the body of the recipient responds to the introduction of foreign tissue into the body by attacking the new organ. All this is not necessary when transplants take place between identical twins as their bodies will not reject organs implanted from one to the other.

    Sample collection

    Twin testing is a quick and simple DNA test. All that the test seeks to establish is whether the twin siblings tested have identical DNA profiles. Of course, if the profiles are the same, then the twins are monozygotic.
    The DNA samples for this type of test are very simple to collect. Normally the DNA testing company will send out a home testing kit. Inside the kit, one will find oral swabs for both twins. These swabs need to be rubbed inside the mouth for ten or fifteen seconds and then left to dry. Once dry they can be returned for laboratory analysis. A twin test is 100% accurate at confirming whether twins are identical or fraternal.

    Twin Chimerism

    Could you imagine having a blood test and doctors telling you have two different blood groups? Or perhaps two different DNA profiles? Twin chimerism is a rare but fascinating phenomenon and would in fact often result in an individual having two blood groups or two genetic blue prints. A chimera twin results when two independently fertilized eggs actually fuse together becoming one single egg. This means that the single egg formed has copy of genetic material from each of the two independently fertilized eggs. Blood chimera twins, where some individuals have more than one blood type, are more common then genetic chimeras. Genetic chimeras are far rarer but Oregon National Primate Research Center in Beaverton has managed to create monkeys with six different genetic blueprints. In humans, the exceptional cases of genetic chimerism result in an individual having two genetic blueprints. Perhaps, there might be people with two, three of even four genetic profiles in their blood cells but we have not as yet discovered them.

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    Article provided by Home DNA Direct.
    www.homednadirect.com

    *This is a sponsored post, paid for by the advertiser. Twinstuff.com has been compensated for this post. The embedded link in this article will take the member to an external website not affiliated with Twinstuff.com. Twinstuff.com receives no royalties for sales resulting from this post.
     
  2. rayceryin12

    rayceryin12 Well-Known Member

    Thanks for the info!
     
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