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Semi identical twin test

A semi identical twin test can determine whether or not your twins are half-identical. This form of twin is extremely rare and has only ever been identified twice.

This latest category of twin joins the better-known classifications of identical and fraternal. Identical twins are formed from a single fertilized egg, which went on to split into separate embryos. This means that the siblings share 100% of their DNA and they are known as monozygotic. The twins can be either two identical boys or two identical girls.

Non-identical (or fraternal) twins are the result of separate fertilized eggs and are known as dizygotic, which means they have two zygotes. This produces two genetically unique siblings, which are no more alike than any other sister or brother. These twins may be both boys, both girls, or one of each, and they share 50% of their DNA. 

Semi identical twins are the result of a single egg being fertilized by two sperm – something that shouldn’t happen. Usually, once a sperm enters the egg, the egg locks down in order to prevent another sperm from entering. This results in three sets of chromosomes, rather than the standard two: one from the mother and two from the father. These twins are known as sesquizygotic.

According to the geneticist Vivienne Souter, of the Banner Good Samaritan Medical Center in Phoenix, Arizona, “Their similarity is somewhere between identical and fraternal twins”. “It makes me wonder whether the current classification of twins is an oversimplification.”

Dr Souter was involved in the first documented case of semi identical twins in 2007. She and her team investigated the twins’ genetic makeup because one was born with ambiguous genitalia. This twin turned out to be a ‘true hermaphrodite’, with both ovarian and testicular tissue. The other twin was anatomically male.

Genetic tests revealed that each twin contained some female cells with two X chromosomes, and some male cells with an X and a Y. According to the researchers, the proportion of each type varied from tissue to tissue in each twin.

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Semi identical twin test from AlphaBiolabs

Although, semi identical twins are incredibly rare, semi identical twin testing is possible from AlphaBiolabs. Its twin test can determine whether your twins are identical or non-identical, and can be adapted to test for semi identical twins too. A testing kit can be sent direct to your home with full instructions on how to collect your samples.

Zygosity twin testing involves analyzing tiny amounts of DNA from inside each sibling’s mouth. All you need to do is rub a large Q-tip on the inside of each twins’ cheek. When these samples are returned to our lab, our scientists examine specific markers present in repeat sections of DNA. The DNA seen at each of these 42 Short Tandem Repeat (STR) loci is compared between the tested individuals; identical twins will share the same DNA profile whereas non-identical siblings will have different DNA profiles.

In the case of semi identical twin testing, your zygosity test can be upgraded to include a DNA analysis of the twins as well as both parents. It is only by analyzing all four samples of DNA that a diagnosis of semi identical twins can be made. Should the initial zygosity test prove your twins to be identical, you can choose to upgrade to the semi identical test.

AlphaBiolabs’ twin testing can be ordered online with results and a keepsake certificate in 3–5 days. An increasing and novel use of a twin test is to use the DNA profile to create a unique gift for new parents, their children, and friends and family. The DNA profile can also be made into exclusive artwork.

This twin test was rated 5 out of 5 stars by – a trusted independent website that gathers genuine reviews from real DNA test customers. To order your test or for more information on Twin testing, please contact us via Live Chat, email or call now at 727-325-2902.

Order a Zygosity Twin DNA Test Online