Can identical twins look different?

Understanding twin DNA: Can identical twins look different?

As a provider of twin DNA testing, we are often asked about the science behind twin DNA, especially when it comes to identical twins.

One of the most common questions is whether identical twins can look different from one another…

Surprisingly, they can! So, how can you ever know whether twins are truly genetically identical?

In this blog, we explain how it is possible for identical twins to look different from one another, how twins who look the same might not be genetically identical, and why a DNA test is the only way to determine whether twins are genetically identical or not!

What are identical twins and how are they formed?

Identical twins – also known as monozygotic twins – are formed when a single fertilised egg splits into two after conception.

They also share the same genetic profile, including the same sex and blood type, and will usually have similar physical characteristics.

However, there are always some physical differences between identical twins. For example, each twin will have a different bite pattern, and different fingerprints; they could also have different handedness (left or right-handed).

There are three medical definitions for the way in which identical twins are formed: dichorionic diamniotic (DCDA) twins, which account for a third of identical twins, monochorionic diamniotic (MCDA) twins, and monochorionic monoamniotic (MCMA) twins.

Fun facts about twins

Identical twins are not carbon copies of each other…

While they might start life with nearly identical genetic blueprints, identical twins can look different from one another.

Identical twins are a product of a single fertilised egg splitting into two, giving them the same genetic material.

And while this shared genetic starting point sets the stage for remarkable similarities in appearance and physiology, the idea that identical twins are perfect carbon copies of each other is a myth.

The differences between identical twins, sometimes subtle and sometimes more pronounced, stem from a combination of genetic, environmental, and lifestyle factors.

This means that a DNA test is the only way to know for sure whether twins are genetically identical or not.

At AlphaBiolabs, we have seen many instances where twins or parents of twins thought they were non-identical, only to find out that they were in fact genetically identical upon taking a DNA test. 

Kelly Coupland, who purchased a test for her newborn daughters, said: “After receiving a lot of comments that our twin girls looked very similar, we ordered the Twin DNA Test from AlphaBiolabs. They are DCDA twins (separate sacs and placentas), so as much as I really wanted identical twins, I thought they’d be non-identical.

“I will never forget the day I saw the email in my inbox. We were so excited to open it and receive the results – they are in fact identical!”

Karen Johnson, who took our Twin DNA Test with her sister, said: “After 50 years of thinking my sister and I looked a lot alike but were fraternal twins, we now know we are identical. The doctor in 1972 thought that because we were in two sacs we must be fraternal – but two sacs are common with identical twins too!”

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Can non-identical twins look the same?

In the same way that siblings from different births can look similar due to their shared DNA, non-identical twins from the same pregnancy can certainly look like one another.

In fact, there have been instances where parents thought their twins were identical, only to discover they were non-identical (fraternal) twins when a DNA test was performed.

As mentioned, the only way to truly know whether twins or multiple birth siblings are identical on a genetic level is with a DNA test.

Identical vs fraternal twins

How can I find out if twins are genetically identical?

Whether you are a twin sibling or a parent of twins, a DNA test is a great way to find out whether multiple birth children are genetically identical or not.

This is especially useful for birth parents who have previously been told that their children are not identical, as many children who do not look alike have in fact been found to be genetically identical when tested!

The same can also be true of twins who are thought to be identical due to looking alike, who are then found to be non-identical. 

Our Twin DNA Test – also known as a Zygosity Test – is performed by collecting a sample of cheek cell DNA from each sibling, using a cheek (buccal) swab.

This non-invasive method of sample collection is simple and completely pain-free, meaning that the test can be performed on a person of any age, from newborn babies to older children and adults.

The twin DNA test is also not exclusive to twin births – we can DNA test up to five siblings from the same pregnancy. Simply tell us how many siblings need to be tested when placing your order*.

You will also receive a DNA certificate detailing the test results and each individual’s DNA profile – a unique keepsake for multiple birth siblings or parents.

Gail Evans, who purchased a twin DNA test for her adult sons, said: “For 26 years we believed that our twin boys were non-identical, as the consultant told me during the scan that the babies were in two separate sacs, and that there were two placentas present.

“Everyone struggled to tell the boys apart, so we decided to arrange a Twin DNA (Zygosity) Test with AlphaBiolabs to clarify the matter once and for all.

“To our surprise, the results confirmed that the boys are identical. This has ended years of speculation within the family and has provided us with conclusive scientific proof.”

Need more information on our Twin DNA Test? Call our friendly, knowledgeable Customer Services team on 0333 600 1300 or email

Twin DNA Test

Find out whether multiple birth siblings are genetically identical, with our at-home DNA test.