Parents of twins are often asked "Are they identical?".  For some people, this is an easy question to answer, but others are not so certain.  We are frequently approached by families who want to know whether their twins are likely to be identical (monozygotic) or fraternal (dizygotic).  Our DNA testing can help you answer this question.

Testing the zygosity of twins, ie. whether they are mono- or dizygotic, involves analysis of bodily samples from both of the twins and their mother and father.  A DNA profile consisting of eight genetic markers  is constructed for each person.  At each of the DNA locations tested, a person will possess two genetic types (alleles).  Each parent will pass one allele onto a child via the egg (mother) or sperm (father).  The two types inherited from the parents thus make up the child's DNA types.

The DNA profiles of the twins are compared.  If their profiles are different they are dizygotic twins with the same genetic relationship as siblings born at different times.  If the twins' profiles are the same in all eight tests they are likely to be monozygotic twins.

If the twins have identical profiles we can calculate the likelihood that the twins are in fact monozygotic rather than dizygotic.  The DNA profiles of the mother and father are examined to determine the possible DNA types of any offspring they may produce.  The chance of detecting a difference between the twins if they are dizygotic depends on the DNA types of the parents.

If the mother (or father) has two of the same alleles at a particular location, then all of her eggs will carry that type, and therefore all her children will have that DNA type.  The more locations at which both alleles are the same, the less likely it is that a difference will be seen between dizygotic twins (or other siblings).

Blood samples are collected by a simple fingerprick method.  This can either be performed by our staff at the VIFM in Southbank, Melbourne, or kits can be sent to the family for blood collection at a convenient location.

Our fingerprick method involves piercing the tip of a finger with a single-use disposable device, as used daily by many diabetics.  A couple of drops of blood are soaked onto a piece of cloth (approximately 1cm x 1cm).  A portion of this blood stain is used in the DNA analysis.  It's that simple!

This collection technique is very easy and the samples are often collected by the parents themselves.  Alternatively, a local doctor may take the samples.  If samples are collected outside of the VIFM, the samples must be transported to our laboratory for analysis.  This is usually arranged by our staff for a small cost (prices are available on request).  Note that biological specimens, including blood stains, cannot legally be mailed via Australia Post.

To proceed with twins testing, the family should contact the VIFM to obtain an application form (or dowload it now Application Form for DNA Twins (zygosity) Testing).  This should be completed and returned to the VIFM with full payment.  Once these are received the parents will be contacted to make arrangements for sample collection. 

Reports of twin testing are usually issued within 5 working days after all samples are received.