Twin Zygosity Test
A twin zygosity test is a DNA test for determining if twins are identical or fraternal. Specifically, this test determines whether two twins developed from the same
zygote
. If the twins developed from the same zygote, then they are identical twins. If they developed from separate zygotes, then they are fraternal twins.
To determine twin zygosity, DNA samples from the two twins are compared. If both samples match at every
locus
, then the twins are identical. If the twins are fraternal, their DNA profiles will be similar, but not necessarily any more alike than two siblings who are not twins.
When is twin zygosity testing used?
Twin zygosity tests are most often performed to satisfy curiosity. Twins are commonly considered identical or fraternal based on how much they look alike or the number of placentas present at their births, but these are not always reliable ways to determine twin zygosity. Many families simply want to know if their twins are identical or fraternal.
Twin zygosity tests have also been used during health problems to identify identical twins for potential tissue and organ donation. Since identical twins have the same DNA pattern, they are considered perfect transplant matches for each other.
Who is typically involved?
Twin zygosity testing only involves two twins. No other parties are necessary for this type of DNA test.
How are the samples collected?
Samples can be collected in several ways.
Buccal swabbing
is the most common collection technique, though several alternatives to it exist. Be sure to speak with the DNA testing company you choose to determine the best collection option for your situation.
It is important that you speak with the company through which you plan to take your twin zygosity test before you make a decision on which type of samples to use.
You can learn more about DNA sample collection procedures by visiting the
Sample Collection
page.
How long can the results take?
Most twin zygosity test results can be released in
3 to 5 business days
after the receipt of your samples by the testing company.
How conclusive are the results?
The twin zygosity DNA test is the easiest and most conclusive way to identify identical and fraternal twins. Other techniques used for identifying twins, such as
HLA
and tissue typing or examining placentas at the birth of the twins, may not be as conclusive as twin zygosity testing.
If twins are identical, you can expect a probability of zygosity of more than 99.99%. This number can run as high as 99.999999999% or higher. This means that the twins shared the same zygote during development.
If twins are fraternal, the probability of zygosity will be 0%. This means that the twins did not share the same zygote during development.
What is the typical price range for twin zygosity testing?
The cost of twin zygosity testing depends on the intended use of the test results. If you need the results for legal purposes, you can order a
chain of custody
test for
between $350 and $500
.
If you do not need the results for legal purposes, you can order in-home testing for
between $150 and $300
.
You can learn more about the reasons behind the wide range of testing costs by visiting the
price differences page
.
What else should you know about twin zygosity testing?
You should definitely consider any future use of your twin zygosity test results that you may have before you order the test. You can learn more by visiting the
Do you need a chain of custody test?
page.
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