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| how does DNA testing
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Paternity (maternity) testing
DNA testing relies on comparing fragments of DNA (called “genetic
loci” or simply “loci”) between an alleged parent and a child. A child
receives one half of his DNA from the mother and the other one from
the father moreover, the process is more or less random. This means
that approximately half of all genes between a parent and
his/her child are identical. If we compare a fragment of DNA between
an alleged parent and the child it has a 50% chance to be identical. If
we compare 12 different fragments, then, according to statistical laws
approximately 6 of them will be identical. In such a case the
probability that the alleged parent is a true biological parent of the
child will be 99.99%. In contrast, if none or 1-2 of the loci studied
turn out to be identical, then the probability of the individual being
a true biological parent of the child is no higher than for any other
person on the street, meaning that he/she is biologically unrelated to the child.
Two factors affect the accuracy of testing – the number of genetic
loci tested and their nature. More then 99% of DNA is identical
between all people and if it was analysed there will be no difference
found between any two individuals, men or women, randomly taken.
However, there are certain areas of DNA which are unique for each
individual (this is to a large degree what makes people different) or found only in a small
number of individuals. Among those, areas of highly variable DNA
called STR or simple tandem repeats are the ones which are commonly
used for DNA testing and people identification. All this means that
the more genetic loci (like STR) are checked the higher will be
the probability of confirming paternity or maternity. Medical Genomics
is currently analysing 16 STR loci for each DNA sample, which gives us
a probability of 99.9999% in confirming alleged paternity (maternity).
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Close Relative Testing (Grand
Parent/Uncle/Aunt/Niece Nephew)
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There is no difference in the testing procedure between this type of
test and paternity (maternity) testing. The only exception is that in
order to achieve a reliable accuracy more genetic loci have to be
compared. This is because a grand parent shares only 25% of his/her
genes with an alleged grand child, uncle and aunt also share 25% of
their genes with the alleged nephew/niece (this is assuming, of course,
that they are not twin brother/sister of the person in question’s
father or mother and also that they are all from the same parental
line) etc. Taking example from the above section, out of 12 loci
analysed approximately 3 should be identical between an alleged grand
child and the grand parent.
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Half Siblingship/Full Siblingship Testing
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Full siblings obtain DNA from the same mother and father and have most of
it in common, though there will be slight variation in the genes they
inherited from a particular parent. In contrast, half siblings will
share only 50% of DNA in common. By analysing DNA from two individuals
it will be possible to unambiguously conclude whether they are half or
full siblings.
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Twin (Zygosity) Testing
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Twins can be of two types – identical, born when the egg divides into
two separate cells straight after being fertilised by a single sperm
and each cell then develops into an embryo, and fraternal, which are
produced when there happened to be two eggs in the womb which are
fertilised by two sperms. Identical twins are always of the same sex, have
absolutely identical DNA and it is impossible to find any genetic
difference between them (they are virtually clones of the original
fertilised egg). Fraternal twins not need to be of the same sex and
have minor differences between their DNA. Using state of the art DNA
analysis of highly variable STR loci Medical Genomics is able to
determine whether two individuals are identical or fraternal twins.
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Y-Chromosome Testing
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Y-chromosome is transmitted by fathers to their male offspring only.
It is highly variable between human population and by analysing
fragments of Y-chromosome from two or more male individuals it is
possible to determine whether they all share the same male ancestors,
how close is this relationship and are they all part of the same
family (so called “surname test”). This analysis is commonly used for
genealogical purposes. Being at the cutting edge of high-tech
genealogical research Medical Genomics compares 26 STR found on
Y-chromosome and gives a conclusive report on whether two (or more)
male individuals are related and how close is the relationship.
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mtDNA Testing
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People inherit mitochondrial DNA (mtDNA) from their mothers. This is a
convenient tool for studying human migration patterns, evolution,
maternally linked relationships and people identification.
Mitochondrial DNA has two highly variable regions, called HVR-1 and
HVR-2. Medical Genomics determines the structure of HVR-1 in all
individuals in question and then compares the results to the generally
accepted standard - the Cambridge Reference Sequence. This analysis
allows us to give a definite and conclusive answer whether the
individuals tested are related, belong to the same ethnic group and to
the same maternal genealogical group.
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