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Twin Zygosity Test

DNA Zygosity Test For Twins

How Can I Tell If My Twins Are “Identical” Or “Fraternal”?

This Is The Question We Hear The Most From Parents Of Twins!

Most people assume that being a twin means having a similar physical appearance. However twin type is determined long before the twins are born. The terms identical and fraternal are common words that refer to “zygosity.” Zygosity is the characteristics of the cell union that happen at conception, which results is the genetic relationship between two twins. With respect to genetic similarities or dissimilarities, twins are classified as identical or fraternal.

When one egg is fertilized by a single sperm cell and then splits, two identical, or monozygotic, twins will result. These twins are referred to as identical since the sequence of the twins’ DNA is identical. Identical twins must be of the same sex. Importantly, the term “identical” often does not apply to the actual physical or behavioral similarities between identical twins. However, identical twins tend to be very similar for traits such as hair color, hair texture, eye color, height, and weight.

When two eggs are independently fertilized by two sperm cells, fraternal or dizygotic twins result. Fraternal twins do not have identical DNA but will have half of their DNA in common, just like siblings of the same parents that are born at different times. Fraternal twins can either be of the same sex or different sex. It is interesting to note that, although there is some evidence that twinning is heritable, neither family studies nor molecular-genetic data suggest that it is either autosomal or sex-linked. 

The only 100% accurate way to determine identical or fraternal twins is by a DNA Zygosity Test.

What Is A Zygosity Test?

Since the above definition of an identical or fraternal twin refers only to the similarity or dissimilarity of the twins’ DNA, a zygosity test is a comparison of the DNA between two twins. At Journey Genetic Testing, our lab analyzes regions of DNA which are called microsatellites. These are stretches of DNA that repeat over and over again, like AACT AACT AACT AACT.

All humans have repeating stretches of DNA, and the repeats vary from one individual to another. When several of these repeat areas are the same between two siblings, it is probable they are identical twins. If the twins are different at one or more repeat markers, they are considered to be fraternal twins. Interestingly, these are almost the exact same techniques used in forensics and in paternity tests. The genes analyzed are not related to any specific physical trait such as hair color, height or personality. 

Zygosity testing works on multiples of any age, newborns to adults. The simple and non-invasive swabbing procedure allows for the rapid and painless collection of a DNA sample.

How Much Does A Twin Test Cost?

Our goal is to make our genetic testing as affordable as possible without compromising on quality. We know that some companies are advertising they offer cheap Twin Zygosity DNA test prices. We want to encourage you to be careful when considering these companies. Cheap DNA tests may have a lot of hidden or surprise costs (for example: a very high cost for more than one DNA kit, an extra charge to provide results to except by phone, etc.). A cheap DNA test usually will cost you more when everything is done, and they often don’t have the resources and trustworthiness of established DNA testing companies like ours.

We don’t offer cheap DNA services. However, we do offer very a very affordable identical twin DNA test. If fact, we have not increased the cost to our customers in over five years, even though our costs have risen along with everything else. Our affordable prices have allowed us to process thousands of DNA samples every year for lawyers, physicians, adoption agencies, and private individuals.

The cost for our DNA test to see if twins (or other multiples) are identical or fraternal is only $109.00.

How Accurate Is Identical Twin Testing?

The only way of knowing if two or more multiples are identical is by doing a zygosity DNA test. Our twin Zygosity DNA test will determine if your twins are identical (monozygotic) or fraternal (dizygotic). The results of this test are 100% accurate, giving you a clear yes or no answer to this question.

While the testing is 100% accurate, and will give you a definite answers, that doesn’t mean that identical twins don’t share 100% of their DNA. Sound confusing? Let look at why we say this. Identical twins form from the same egg, and they get the same genetic material from both mom and dad , but that doesn’t mean they’re genetically identical by the time they’re born.

Monozygotic twins may pick up what are called genetic mutations in the womb. These mutations are nothing to be concerned about. This terms means that as their cells create and blend new strands of DNA they split into more and more cells. It is estimated that, on average, a pair of twins have genomes that differ by an average of 5.2 mutations that occur early in development. They share enough DNA to be called identical, even with the slight mutations.

The Need For Twin Zygosity Testing

Most people order a zygosity test to satisfy their curiosity, and that of their friends and family. However, there are some health conditions with where it would be useful to know if a condition experienced by one twin will be likely to be experienced by the other twin. Identical twins can donate organs to each other in certain situations. For important medical decision making, we recommend have a legal, chain of custody twin test done. Since the laboratory is AABB accredited, it just requires having an authorized DNA collector take the DNA samples, and complete a chain of custody. If you have a need for a legal document proving zygosity, please talk with one of our Genetic Consultants and we can set everything up for you.

How Long Will It Take To Get My Twin DNA Test Results?

Testing for Twin Zygosity can begin once the DNA samples arrive at the lab. If samples are being sent from more than one location, testing begins when the last sample arrives. We send you an email notification that all samples have been received, and that testing has started.

Twin Zygosity DNA test results are usually available in just 1 business days. This means if we start testing on a Monday, your results should be ready and sent to you on Tuesday, by the end of business. While uncommon, there are some circumstances that may case a slight delay in this time frame. A delay may occur if:

  • extended testing is needed to examine more genetic markers (this does not happen often);
  • you have sent something other than a mouth swab for DNA testing which requires a viability test before regular testing can begin.

Your identical twin DNA test samples are always run twice to verify the DNA profiles being reported before the results are issued. Twin Zygosity test results are reviewed, and confirmed, by a lab Ph.D., who is required to sign the results report. It is only after all of this that the report is to sent you. A report that is not reviewed, or signed, by a Ph.D. in genetics, whether for private results or a court ordered test, is something we will not provide and we would not trust those results.

The report with answer as to if your twins or triplets are identical or fraternal will be 100% accurate. We do not guarantee a specific result, only accurate ones.

Your results will be sent to the email address on your order form in a .pdf format. All reports are written in easy to understand language. If you want a permanent copy of the report, you can either print the PDF, or order a printed hard copy mailed to you.

Limitations of Zygosity Testing

There are two instances where Zygosity DNA testing has not developed to the level of accuracy we require. Because of this we are unable to perform the testing in these instances:

  • Suspected mirror image twins. Mirror image twins are identical twins that result when a fertilized egg splits later in the embryonic stage than usual, typically from day 9 to 12. Mirror image twins tend to exhibit characteristics with reversed asymmetry (e.g., one twin is left-handed and the other is right-handed). If this split happens much later than this, then the twins can be co-joined. A DNA-based zygosity test cannot determine is twins are mirror image twins. 
  • Polar body or “half-identical” twins. Polar body twins are believed to occur when the mother’s egg splits before fertilization and one half (referred to as the ‘polar body’) is also fertilized by a different sperm. This results in twins who share half their genes in common (from the mother) and the other half different (from the two sperm). They share some features of identical twins and some features of fraternal twins and are so-called half-identical twins. However, DNA-based zygosity tests are currently not available to determine if twins are polar-body twins

Benefits Of DNA Zygosity Testing Through Journey Genetic Testing

Utilizing the most advanced technology. along with standardized methods in human identity testing, our results are guaranteed to be 100% accurate. Ensuring this level of accuracy and quality control is of the utmost importance to us.

Specialization in zygosity testing allows us to offer these services at a fraction of the cost of what many testing laboratories charge. We are able to provide you access to the highest quality genetic testing services that were once out of reach because of high cost.

Our clients receive their customized DNA collection kits in one to three business days, depending on location. Once the samples are returned using the prepaid overnight FedEx mailer (USA addresses only for the return mailer), the laboratory immediately begins testing, and provides the results in just 1 business day in 99.8% of our cases. These are emailed to you the same day they are released in an PDF that is easy to read and understand.

Often Asked Questions About Twin Zygosity Testing

home twin test kit

Twin Zygosity FAQs
How Common Is Twinning?

Approximately 30 out of every 1,000 births in the United States produce twins. One of every three sets of twins is identical.

Can Identical Twins Have Different Blood Types?

The answer may surprise you. Yes, in very rare circumstances identical twins can have different blood types. This has been proven by testing we have done on a set of identical twins.

Can Twins Have Different Fathers?

Yes. In rare instances, fraternal twins can actually be half-siblings, with different fathers, even though they are born at the same time. Although the standard Journey Genetic Testing DNA twin test does not include the establishment of paternity, it is possible to determine the paternity of twins by testing their alleged father(s) or possibly by conducting a sibling (full or half) analysis on the DNA data generated from non-identical twins.

Is There A Minimum Age To Take A Zygosity Test?

Zygosity testing works on multiples of any age, newborns to adults. The simple and non-invasive swabbing procedure allows for the rapid and painless collection of a DNA sample.

My Physician Already Said My Twins Are Fraternal. Why Should I Do This Testing?

Almost 33% percent of the time when there are two sets of membranes (i.e. dichorionic) identified at delivery, the twins are actually identical and not fraternal. If the fertilized egg splits prior to 2 days after conception, two complete placentas and two sets of membranes are formed causing dichorionic placentation. This is a common misunderstanding that leads to incorrect zygosity classification. This is true regardless if the dichorionic placenta is fused or not. Unless a DNA test is performed, it is difficult to definitively determine if like-sexed dichorionic twins are fraternal.

What If The Twin Live In Different Locations?

No problem! Just indicate on your order form that you need more than one DNA kit. You will then enter the addresses to send the home Twin Test kits to. They will both be coded with the case number to be matched at the lab. And it’s ok if one set of swabs come in to the lab before the other – we will just store it in a safe way and then start testing when all samples have arrived.

Our Client Twin Zygosity Test Reviews

Highly Recommend!

Rated 5 out of 5
January 31, 2023

Their staff is so acknowledgeable, patient and polite. Journey Genetic is very thorough with the samples that are sent in. I was able to do sibling test, a paternity test with out the father to find out if my two kids had the same father, since we were separated for awhile. You’ll know every step of the process. The results came back in 2 days. And to answer the question YES both my kids have the same dad! I highly recommend them.



Rated 5 out of 5
January 30, 2023

Could Not Have Been Easier


Peace of mind

Rated 5 out of 5
January 27, 2023

Peace of mind is priceless and this dna home paternity kit gives you that


Journey Was Great!

Rated 5 out of 5
January 23, 2023

I don’t know where to start! Affordable, very simple step-by-step process, on-time if not early results, you choose how you want your results, very confidential & secure & the tracking/email alerts was a major plus for me! I wouldnt look or shop no further than this test, it’s worth every penny & to mention the high accuracy!!! This DNA results really brought peace & an ease of mind!


Strongly Recommend

Rated 5 out of 5
January 19, 2023

The process was so simple to understand. The service was fast. The result was back in 2 days. Now I am at peace. This is priceless. Every doubting grandparent should do it. Peace of mind is priceless.

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