Sibling and Relationship Testing

Who can be tested?

DNA testing can be performed on individuals that share common relatives e.g Full or Half Siblings, Aunts, Uncles, Nieces, Nephews, Grandparents, Cousins etc.


Why would I test an extended relationship?

For some people direct testing of parent – child relationship may not be possible, this may be because the parent is deceased, unavailable or unwilling to participate in testing. In such cases extended relationship testing can be carried out to determine if the persons involved in testing are related.

However, the more extended the relationship the harder it is to determine the relationship as they will share less and less genetic material. We each have 2 copies of 22 chromosomes in our body, one copy is passed on from the mother and the other from the father. To determine paternity or maternity we look for direct matches between the parent and child. For other relationships there is no direct genetic inheritance and so it is harder to determine a relationship.


What type of testing can be performed?

There are 3 possible types of extended relationship tests that can be performed

1. An Extended Relationship Analysis – Profiles of the tested persons will be generated and a statistical model and database is used to calculate how likely it is for the alleged relationship to exist.

2. Y-STR testing – For males that share the same paternal line, looking at their Y-Chromosome which is passed on virtually unchanged through the paternal line can establish relationship (e.g grandson and paternal grandfather)

3. mtDNA testing – For persons that share the same maternal line, looking at their mitochondria which is passed on virtually unchanged through the maternal line can establish relationship (e.g niece and maternal aunt or grandson and maternal grandmother)



Extended Relationship Testing cannot give a conclusive result of a relationship. Degrees of confidence in the result can be given only and this gives a result that there may be a greater chance of a relationship between individuals than testing random individuals in the population.  However, a certainty of there not being the possibility of a relationship can be shown for some individuals.

The results will show:

The likelihood ratio is less that 1 – no relationship can exist

The likelihood ration is more than 1 – the greater the number above 1, the greater the strength of the probability of a relationship

Please call DNA QLD to discuss your particular case.  DNA QLD advises that the result may be inconclusive for an extended relationship test.  This is not due to laboratory error but as shown above, in difficulty in comparing individuals in extended relationships.

**No refund on testing costs will be available for this testing if the result is inconclusive.

Under current Australian law, testing results from sibling or grandparent testing are not accepted as proof of a relationship for the Family Law Court of Australia, for changes to a birth certificate or for wills and estate matters.

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