Paternity Testing
Using Forensic DNA Technology to Identify a Child's Father
A look into how scientists can use forensic DNA technology to identify a child's biological father.
Paternity testing is a technique used to help establish the identity of a person’s father by looking at the DNA of their mother, the man claimed to be the father and the child. This technique can help resolve paternity, probate and immigration issues.
Each person’s DNA is unique, unless you are an identical twin. Half of the DNA is inherited from the mother and the other half inherited from the father. When the identity of the father is questioned, it can be established by comparing the child’s DNA with the DNA of its mother and the DNA of the possible father.
To carry out a paternity test DNA samples from the mother, the claimed father and the child are taken. The samples can be in the form of a mouth swab or blood from a finger prick, for example. DNA is then extracted from the cells in each sample. The DNA from each sample is then processed and analysed to obtain a DNA profile for each person involved. The DNA profiles are then compared. Remembering that half of the child’s DNA will be from its mother and the other half from its father, the profiles are then checked against each other. The parts of the child’s DNA profile that have come from its mother are identified, thus leaving the remaining half of the child’s DNA to have been inherited from the biological father.
If the components identified as being the father’s in the child’s DNA profile do not match components in the claimed father’s DNA profile, then the man in question, with 100% probability cannot be the child’s father.
If the components identified in the child’s DNA profile to have come from its father do match the components in the claimed father’s DNA profile then there is a 99.99% probability that the man in question is the actual father.
To give a simplified example, where the letters represent components of the DNA profiles of the people involved:
Mother AB
Claimed Father CD
Child AD
The child must have received the A component from its mother. The child could not have received the D component from its mother, as the mother does not have the D component in her profile, so therefore the child must have received D from its father. The man claimed to be the child’s father has a D component, therefore it is possible that the man is indeed the child’s father.
To give another example:
Mother AB
Claimed Father CD
Child AE
Again, the child must have received the A from its mother, but it could not have received the E from its mother, as the mother does not have the E component, so therefore the child must of received E from its father. However, in this example, the claimed father does not have the E component either and therefore he cannot be the father of this child.
‘Motherless’ testing is also possible, where samples are only taken from the claimed father and the child; however this gives slightly less accurate results.
Sources:
Questioning Paternity, The Forensic Science Service
How do I get a paternity test, NHS Direct
Paternity test, DNA Diagnostics Center
