Twin Tests (Zygosity Testing)
Twin Testing Summary
Twin DNA testing, also called zygosity testing, determines whether twins are identical or non-identical. Identical twins develop from the same fertilised egg and should have matching DNA profiles at the tested markers. Non-identical, or fraternal, twins develop from separate eggs and have different profiles, much like other full siblings.
The test requires a cheek-swab sample from each twin. Parental samples are not normally needed. The laboratory compares the twins’ profiles across the analysed markers and reports whether they are genetically identical or non-identical.
At thatDNAcompany®, the current published UK twin test costs £85 and includes a discreet kit, a paid return envelope, UK laboratory processing and results in two working days after the samples reach us. Separate-address kits can be arranged when the twins do not live together.
- 2 working day results available from £85*
- Discreet sampling kit to a single address. Option to send additional kit to separate address if required.
- Paid return envelope included as standard.
- UK based customer service and laboratory. We will never send your samples to another company for processing
- No parental samples required.
* From the time we receive your samples in the laboratory.
Understanding Twin Zygosity DNA Testing
Sometimes it is obvious that twins are non-identical, for example, where they are different biological sexes. In many same-sex twin pairs, appearance alone cannot establish zygosity.
Twins may look remarkably similar without being identical, while identical twins can develop differences in height, weight, health, fingerprints, hairstyle and personality. A zygosity test answers the genetic question directly.
Identical and non-identical twins
Identical twins are also described as monozygotic because they originate from one fertilised egg that divided. Non-identical twins are dizygotic because they originate from two separately fertilised eggs.
Non-identical twins share, on average, the same amount of DNA as other full siblings. They may inherit many of the same variants, but their overall tested profiles will not be identical.
How the laboratory test works
Each twin provides a cheek-swab sample. The laboratory builds a DNA profile from the selected markers and places the two profiles side by side.
Where the profiles match across the required markers, the result supports identical twinning. Where the twins display the differences expected between siblings, they are reported as non-identical.
Our service currently examines approximately 23 markers and describes the result as conclusive for determining whether the tested twins are identical or non-identical, based on the samples received.
Choosing a twin testing company
Look beyond a headline promising a “fast kit.” Check:
- Whether the provider operates or clearly identifies the laboratory.
- Whether all analysis is included in the price.
- How return postage is handled.
- When the turnaround begins.
- How reports are delivered.
- Whether separate kits can be sent.
- What happens if a sample does not contain enough DNA.
A two-day laboratory service does not mean the entire process takes two calendar days. Delivery to the twins, return postage, weekends and bank holidays must be added to the laboratory turnaround.
What twin testing is not
Zygosity testing does not investigate whether two individuals share the same father unless the question is specifically structured as a sibling or paternity case. It also does not provide medical screening, ancestry estimates or information about future health.
Its purpose is focused and straightforward: to establish whether the tested twins are genetically identical or non-identical.
Twin Testing FAQs
What is twin DNA testing?
It is a laboratory comparison of DNA from two twins to determine whether they are genetically identical or non-identical.
Where can I get twin DNA testing in the UK?
A home zygosity kit can be ordered directly from a specialist UK relationship-testing laboratory. That DNA Company currently provides postal kits processed through its UK service.
What is twin zygosity DNA testing?
Zygosity testing is the scientific name for determining whether twins are monozygotic, meaning identical, or dizygotic, meaning non-identical or fraternal.
Where can I order an at-home twin DNA testing kit?
You can order a personal twin test through thatDNAcompany®. Swabs are collected at home and returned in the supplied paid envelope.
How much does twin DNA testing typically cost?
Prices depend on the laboratory and delivery options. Our currently published twin zygosity test is £85, including the standard kit, return envelope, processing and report.
What are the most reliable twin DNA testing services?
Choose a provider that performs a genuine side-by-side DNA profile comparison, identifies where the work is completed, explains the number of markers used and supplies a written result rather than relying on appearance or a questionnaire.
Which companies offer the fastest twin DNA testing?
Several companies advertise expedited services, but compare the laboratory turnaround rather than the marketing headline. That DNA Company currently states two working days from laboratory receipt of the samples; postal time remains additional.