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Frequently Asked Questions (FAQ)
What
is DNA?
DNA carries our hereditary information. It is
present in most cells of every multicellular
organism. It is in fact a very long sequence
of nucleotides, the building blocks of DNA.
In DNA we find 4 different nucleotides (base
pairs).
Just like digital information is represented
as a sequence of zeroes and ones, genetic information
is represented by a sequence of nucleotides.
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How does a DNA paternity test work ?
Every person has two copies of each gene. One copy comes from the mother and the other copy comes from the father. Thus, one half of the genetic material in our body is inherited directly from each of our two parents. When a DNA- paternity test is performed, our DNA laboratory examines the DNA of the child to determine whether the father's contribution matches that of the alleged father. If the alleged father is the true biological father of the child, half of the child's genes will match that of the alleged father's. The other half comes from the mother and will match the profile of the mother (testing the mother is optional). If the tested man is not the biological father of the child, the half of the child's genetic material which comes from the father will not match the DNA-profile of the tested man. If the DNA-profile does not match, the tested man is excluded as being the true biological father of the child. When a DNA paternity test is performed, the laboratory usually examines many different genetic locations. The more genetic locations that are examined, the more powerful and accurate your test becomes. After examining many genetic locations, a DNA lab can conclusive determine whether the tested man is indeed the true biological father of the child. Our paternity test report will provide you with a simple "yes" or "no" conclusion for your paternity test as well as a detailed report indicating the DNA-profiles of each tested individual.
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How
can people be identified on the basis of their
DNA?
Most living organisms grow from one cell —the
fertilized egg cell—, which by multiplying
itself eventually gives rise to all cells that
make up the adult individual. Roughly one could
say that every cell of an individual contains
the same genetic information, i.e., every cell
of a multicellular organism has identical DNA
content.
However, the DNA content of different individuals
is (slightly) different.
When DNA from separate individuals is compared,
discrepancies can be found. These discrepancies
can be used to determine the relationship between
those individuals.
Similarly, when samples have identical DNA contents,
they must come from the same individual.
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What
is a genetic locus or marker?
Since it is not possible to analyze
all of a person's DNA, in practice, specific genes are selected for analysis. These genes typically do not code for any physical property of the individual, but are chosen for their properties of being easily analyzed and having a high discriminating power in identification and consanguinity analysis.
A genetic marker is a piece of DNA (or a gene) that everyone has,
but that can, in each individual, be one of a few different forms that occur in the population (alleles). The pattern of alleles that a person carries for set of genetic markers is called a DNA profile.
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What
is a DNA profile?
The pattern of alleles that a person carries for set of genetic markers is called a DNA profile or a DNA-fingerprint. A DNA profile is similar to a real fingerprint in
that its pattern is unique for each individual
and hence can be used to unequivocally identify
an individual. DNA profiles are comparable only
if they describe the same loci. Comparison of genetic fingerprints can yield information on consanguinity because each half of our genotype for every genetic markers is inherited from one parent.
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What
is the "matching probability"?
The matching probability is a value that is given to the chance of a false positive identity match when comparing two DNA profiles. The more genetic markers that are compared, the smaller the chance of a false positive match.
To clarify this concept, we present a simple
example.
If one were to investigate locus A whose variants
A1 A2 A3 A4 and A5 (=alleles) occur with equal
probabilities (1/5) in the population, then comparison of two samples may show that these samples match. That means they contain the same set of alleles and both samples may be from the same individual. Assume that the matching samples each contain the A1 and A2 alleles for the A gene. Knowing that any allele of the A gene has a one in five chance of being A1, the frequency that the A1A2 genotype will occur in the population is the product of (the chance that A1 will be one of 2 alleles) and (the chance that A2 will be one of 2 alleles). The chance that A1 will occur in any two alleles tested, is calculated as (2X(1/5)-(1/5)^2)=36% . The chance of A2 being in-there is the same (36%), since the population frequency of A2 is 1/5 also. The chance of finding both A1 and A2 in any two alleles analyzed for the A gene is therefore 36%X36%=12.96%.
All this means is, that when you find the genotype of a person for gene A to be A1A2, the chance that you will match this profile with a sample from any random individual, is about 13%.
If in addition a locus B is investigated, whose
variants B1 B2 B3 B4 and B5 are also uniformly
distributed, then the chance that two individuals
carry two matching genes is reduced
to 1.6%. With 3 loci this probability
is only 0.2% and with 4 loci it is 0,03%. with 15 genetic markers, it is 4.9e-14.
This example is somewhat simplified in that the variants of a gene are not equally frequent,
and there are usually more than five variants.
The standard STR loci that are used for identification are chosen for their high discriminating power. The matching probability of an identity profile with the 13 codis markers, D16S539, D2S1338 and amelogenin is no more than 1 in 50 billion, which is astronomically small. The chance of a cosmic ray changing a DNA profile when it is being processed by hitting the RAM of a computer, is probably higher.
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What
are STR analyses?
STR stands for Short Tandem Repeats or short
equally oriented repetitions in the DNA sequence.
STR loci are loci whose alleles differ in the
number of repetitions of successive base pairs,
which makes them easier to distinguish because
the difference between two alleles is an integer
multiple of the length of the repetition. The
loci that are in standard use in the forensic
world and that are used in the big DNA databases
of international law enforcement agencies and
the FBI, are all STR loci.
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How
much DNA is required for a successful analysis?
All
we need is 0,5 ng, i.e., half a billionth of
a gram DNA. That's a very tiny amount!
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What is
a sample kit and how do I obtain a sample?
You may order a kit using our
web form, or by telephone at +32-485-471309.
The kit contains everything you need to take
one or more samples under optimal conditions.
These should then be forwarded to us.
I have a hair/cigarette
but/stain/... that needs to be analyzed. What
now?
If you already have our sample kit, just follow
the enclosed instructions and put the sample
in the tube, label the kit and mail it to us.
Make sure that you are familiar with the legal
issues concerning privacy, in particular which
approvals are needed for obtaining samples from
each individual (Further
considerations...).
Take care to protect the sample
as much as possible against contamination with
other human DNA. Try, in the mean time, to keep
the sample dry, to prevent bacterial breakdown
of the human DNA. Use clean tweezers to insert
the sample in the vial.
The cotton swab serves to take
a sample from e.g., you can obtain cells from
the mouth, by rubbing the swab a few times vigorously
against the inside of the cheek. Then put the
swab, cotton end first, in the vial and use
scissors to cut any excess length such that the
vial can be closed.
If you send hairs, try to include
the follicles.
After shutting the vial, label
the sample with a reference number of your choice
(use the label provided with the kit). If necessary
use transparent adhesive tape to fix the label.
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How
soon can the analysis results be available?
Under normal circumstances you will receive
the results from the DNA analysis within a
week after our receipt of the samples. The
limiting factors here are the quality of the
samples and the capacity of the lab equipment.
Express
Service
We can't guarantee
a maximum turnaround time, but in urgent cases,
and with good quality samples
results can be available within 48 hours after
receipt of the samples. The surcharge of 200
Euros for express service
is to compensate for suspending and restarting
the lab's workflow. If we don't make the 48
hours, there will be no surcharge.
Call us at +32485471309 to
discuss how to most efficiently get the samples
to the lab.
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What
kinds of samples can be analyzed?
In principle, anything that contains human cellular
material, even a smear or a smudge, can be used.
To take a sample in ideal conditions,
it is best to use a cotton swab or Q-tip and
rub it gently on the inside of the cheek and
under the tongue (cf. the sample kit for the
parental testing)
Even traces of DNA (very small
quantities) are sufficient for a successful
analysis. A post-stamp that was licked will usually
contain sufficient amounts of saliva to contain
human cellular material. A cigarette but, a toothbrush, the stick of a lollipop, a dummy teat, a
razor blade, a stain on underwear, scales of
skin from a sheet or pillow case, a used handkerchief,
a worn garment, a used condom, 0.1 ml of urine, a blood
stain on paper or cloth are acceptable as well. These are all
examples of samples that can yield DNA profiles
and can serve for identification or kinship
analysis.
Hair should have hair roots. A single hair root may not contain enough DNA for analysis. Just like hair shafts, fingernails contain very little or no DNA.
It is important to know that the situation gets more complicated, and more difficult to interpret, when DNA from different
people is present in a single sample.
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How
long will a sample retain its quality?
DNA is quite stable, and, under most circumstances
can be stored for a long time with no degradation.
It is always a good idea to keep samples dry.
Humidity can cause bacteria and fungi to grow, and consume human DNA traces.
So send your samples quickly, or dry
them first!
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