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Determining the zygosity of twins can establish whether or not they are identical or fraternal.

  • Identical twins are formed from a single fertilised egg, which went on to split into separate embryos. This means that the siblings’ DNA is exactly the same and they are known as monozygotic.
  • Non-identical (or fraternal) twins are the result of separate fertilised eggs and are known as dizygotic, which means they have two zygotes. These babies are no more alike than any other brothers or sisters, and may be both male, both female, or one of each. They share DNA in common as in the case of brothers and sisters.

However, it’s not always clear what’s happening in the womb. Identical twins, for example, don’t always share the same placenta and sac: it all depends on when the eggs splits.  

Usually, by the time twins are around 2 years of age, their zygosity may be quite clear from their physical features. For example, their eye and hair colour, ear shape, teeth formation, hand and feet appearance can indicate whether or not they are identical. However, some identical twins, don’t look exactly the same: there can be minor differences between siblings that lead their parents to believe they are non-identical.

If changes in physical features aren’t apparent, the only way to determine the zygosity of twins is by zygosity twin testing. This scientific method can help determine whether twins are identical or not.

Determining zygosity of twins in your own home

AlphaBiolabs can send a zygosity twin testing kit direct to your home with full instructions on how to collect your samples.

Zygosity twin testing involves analysing tiny amounts of DNA from inside each sibling’s mouth. All you need to do is rub a cotton bud on the inside of each twins’ cheek. When these samples are returned to our laboratory, our scientists examine specific markers present in repeat sections of DNA. The DNA seen at each of these 35 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.

The Twin DNA test costs just £99 for next day results and includes a Zygosity Certificate.

An increasing and novel use of a DNA zygosity profile is as a unique gift idea for multiple birth parents and/or their children. Same day results are also possible for an extra £70.

For more information on Zygosity twin testing, please contact AlphaBiolabs’ Customer Service team on 0333 600 1300, email: or visit our website at

Order a DNA test

AlphaBiolabs is an award-winning DNA testing lab. DNA testing starts from just £99.