Sibling
DNA Testing is used to determine
whether two (or more) individuals
have common biological parents.
This test is an indirect
way of establishing Paternity
or Maternity.
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Results available within 7-9 days
of samples reaching our laboratories.
This is due to the additional statistical
analysis needed in these cases.
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Sibling analysis is divided
into two categories
Full-Sibling Study
- This test is ordered for Clients
who want to determine if they
have both parents in common (share
the same mother and the same father).
- The cost of the test includes
2 Siblings.
- Additional Siblings will
each be charged at the additional
person rate.
Half-Sibling Study
This test is ordered for Clients
who want to determine if they have
one parent in common. (Share the
same mother or the same father)
- The cost of the test includes
2 Siblings.
- Additional Siblings will
each be charged at the additional
person rate.
How does Sibling analysis
work?
During a Sibling DNA test, the
DNA profile of each potential Sibling
is obtained and compared to determine
the Full Sib Index, Half Sib Index
and Unrelated Index. These figures
are based on how many of the targeted
areas of DNA are shared between
the individuals being tested and
how likely those matches would be
seen if we were to test members
of the general population with the
same ethnic origin as the test participants.
How are results interpreted?
The values from the Full Sib Index,
Half Sib Index and Unrelated Index
are combined to give a value called
a ‘likelihood ratio’.
Based on the question the client
wants us to answer, this value for
the likelihood ratio tells us which
scenario is more likely.
For example, if two individuals
being tested want to know if they
are half of full siblings, this
figure will indicate how many ‘times
more likely’ the data is if
they are full siblings rather than
half siblings. This value for the
likelihood ratio falls into a range
of categories which are described
in the report. For example, a likelihood
ratio of 132, would provide ‘Good’ evidence
that the individuals in the above
example are full rather than half
siblings, while a likelihood ratio
of 332, would provide ‘Strong’ evidence
that the individuals in the above
example are full rather than half
siblings.
Why is Sibling DNA testing
less accurate than Paternity/Maternity
Testing?
In a Paternity/Maternity test,
exactly half of the child’s
DNA will match the biological father
and the other half will exactly
match the biological mother.
However, Siblings do not have
the exact same DNA, as the inheritance
of alleles from biological parents
is random. At each genetic location
(part of the DNA) a person possesses
two alleles. A person will only
pass one of these alleles to their
offspring. Which allele is completely
random. Therefore one child could
inherit one allele from his father,
while the child’s brother
or sister could inherit the other.
The allele inherited from the father
joins with the allele inherited
from the mother for that genetic
location, when an egg is fertilized
by a sperm. This is duplicated millions
of times along the DNA molecule
to form a child’s own unique
DNA, made from half its fathers
and half its mothers DNA.
The calculation of the Sibling
indexes allows for these differences
and can therefore still provide
accurate and useful results. It
works because true Siblings will
have many more alleles in common
than two unrelated individuals.
The Risks!!
There is always the chance that
the test will yield an INCONCLUSIVE
result. This occurs in approximately
20% of cases when the genetic information
shared between potential siblings
is common in relation to the genetic
information shared by the general
population. This means the scientists
are unable to determine which biological
relationship exists e.g. full or
half sibling.
Clients should be fully
aware of the limitations of the
test before proceeding.
When should Sibling studies
be used?
Usually, a Sibling test is only
carried out as a last resort because
the alleged mother and/or father
are either deceased or unavailable
for testing.
Call a scientist for advice on 0800
032 5945 or contact your
local DNA Clinic to make an appointment.
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site please click
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