Paternity testing
Paternity testing
A paternity test is conducted to prove paternity,
that is, whether a man is the biological father of another
individual. This may be relevant in view of rights and duties of the father.
Similarly, a maternity test can be carried out. This is less common, because
at least during childbirth and pregnancy, except in the case of a pregnancy involving embryo
transfer or egg donation, it is obvious who the mother is.
However, it is used in a number of events such as legal battles where a
person's maternity is challenged, where the mother is uncertain because she has
not seen her child for an extended period of time, or where deceased persons
need to be identified.
Although not constituting completely reliable
evidence, several congenital traits such as
attached earlobes,
the widow's peak,
or the cleft chin,
may serve as tentative indicators of (non-)parenthood as they are readily
observable and inherited via autosomal-dominant genes.
A more reliable way to ascertain parenthood is
via DNA analysis (known as genetic fingerprinting of individuals),
although older methods have included ABO blood
group typing, analysis of various other proteins
and enzymes,
or using HLA
antigens.
The current techniques for paternity testing are using polymerase chain reaction (PCR) and restriction fragment length
polymorphism (RFLP). For the most part however, DNA has all but
taken over all the other forms of testing. Genetic testing usually has a
99.999% accuracy rate, or 99,999 out of 100,000.[citation needed]
DNA
testing
The DNA of an individual is almost exactly the same in each and
every somatic (non reproductive) cell.
Sexual reproduction brings the DNA of both
parents together randomly to create a unique combination of genetic material in
a new cell, so the genetic material of an individual is derived from the
genetic material of both their parents in roughly equal amounts. This genetic
material is known as the nuclear genome of the individual, because it is found in the nucleus.
Comparing the DNA sequence of an individual to
that of another individual can show if one of them was derived from the other
or not. Specific sequences are usually looked at to see if they were copied
verbatim from one of the individual's genome to the other. If that was the
case, then this proves that the genetic material of one individual could have
been derived from that of the other (i.e.: one is the parent of the other).
Besides the nuclear DNA in the nucleus, the mitochondria
in the cells also have their own genetic material termed the mitochondrial genome. Mitochondrial DNA
comes only from the mother, without any shuffling.
Proving a relationship based on comparison of
the mitochondrial genome is much easier than
that based on the nuclear genome. However, testing the mitochondrial genome can
only prove if two individuals are related by common descent
through maternal lines only from a common ancestor and is thus of limited value
(for instance, it could not be used to test for paternity).
Scientific tests can now determine paternity at
12 weeks into a pregnancy using non-invasive testing methods in many cases.
This involves a simple blood sample taken from the pregnant woman's arm. The
pregnant female's blood carries the fetus' DNA which can be compared to the DNA
of the alleged father. Professor Dennis Lo Yuk-ming is the Dr. Li Ka Shing
Professor of Medicine and Professor of Chemical Pathology at The Chinese
University of
In the UK,
there were no restrictions on paternity tests until the Human Tissue Act came into force in September
2006. Section 45 states that it is an offence to possess without appropriate
consent any human bodily material with the intent of analyzing its DNA. Legally
declared fathers have access to paternity testing services under the new
regulations, provided the putative parental DNA being tested is their own.
Tests are sometimes ordered by courts when proof
of paternity is required. In the
Disproving paternity
by use of blood types
A comparison of the blood type of both alleged parents and the child can disprove paternity in some cases. Only certain blood type combinations are possible and a mismatch may prove that the alleged biological father is, in fact, not the father of the child. See the Parent/Child Blood Type Comparison Chart on the website of the Canadian Children's Rights Council.
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