Polymerase Chain Reaction testing usually involves taking a swab from the inner cheek for DNA samples. It is a faster test than RFLP and usually looks at between six and nine loci on the DNA. This test however does not provide the same degree of information as is provided by the RFLP test.
PCR DNA testing works by "amplifying" the sample DNA, or taking a small sample of DNA and then multiplying it. This is useful if only a small sample can be obtained and is also useful for working with degraded DNA. When using PCR DNA testing however the laboratory needs to be particularly careful about preventing contamination within the sample as the amplification process could tend to increase the chances of contamination.
The process of PCR DNA testing involves heating the DNA, adding primers and then cooling it so that it recombines and an enzyme reads the DNA sequence in order to create multiple copies of the DNA. Visit for more info on genetic testing.
The Restriction Fragment Length Polymorphism test takes longer than the PCR test and is a slightly older method but can provide more reliable results as each loci presents more information regarding paternity. It requires a larger sample of DNA and is more likely to use blood for the DNA testing but it can also be done using a swab from the inner cheek if necessary.
The AABB report from 2004 stated that there is a decrease in the number of laboratories using the RFLP method and an increase in laboratories using the PCR method of DNA testing with PCR being used in 98.34% of the cases.
In conclusion, there are two main methods of paternity DNA testing that are mainly used today. These two methods are Polymerase Chain Reaction testing and Restriction Fragment Length Polymorphism testing. PCR testing is used in 98.34% of the DNA testing cases according to the 2004 AABB report and seems to be increasing over the older method of RFLP. PCR is a quicker method of testing and multiplies the amount of DNA material so that only small samples are needed; however this does lead to a risk of contamination. If you are going for PCR testing or ordering a DNA home test kit you should ensure that they are AABB approved and that they offer at least a 99% guarantee and test at least ten loci.
The Twin Zygosity DNA test can determine whether twins are identical or fraternal. Understanding whether a twin is identical or fraternal is not always easy due to possible similar physical resemblance even between fraternal twins. The only way to precisely confirm whether twins are identical or not is through the analysis of the DNA profile of the twins through DNA testing.
Identical or Fraternal?
Identical twins will have identical DNA profiles. Fraternal twins will have different DNA profiles and although they can be relatively similar they will not be identical. Therefore, once the DNA test is performed the profiles are compared to see whether they are identical or not.
Identical twins are formed when one egg is fertilised by one sperm, and then divides and separates into two identical cells creating two individuals with the same DNA profile.
Fraternal twins are born when two different eggs are fertilised by two different sperm. Hence the DNA profile will be different and the twins will be basically normal siblings born relatively close to each other.
When is the twin zygosity DNA test performed?
The twin zygosity DNA test is normally performed primarily for curiosity purposes as the parents or twins will want to confirm if they are identical or not. However, the results of the test may also be required for medical purposes to assess whether one twin can donate an organ or bone marrow to the other twin in the case of a transplant. In such cases, it is important to confirm with certainty whether they are identical or not to confirm the viability of the transplant.
Twin Zygosity testing and DNA Paternity Testing
When performing a DNA paternity test and twins are involved, we normally request that both children are sent for testing as we are not in a position to assess if the twins are identical or not. Technically, the possibility may exist that the mother may have slept with separate men on the same date or in proximity, and have had two separate eggs fertilised by sperm from different donors. In such cases, the two children will have different fathers.
Problems may also arise when determining paternity of a child through a DNA paternity test when the possible fathers are twins and hence have the same DNA Profile. In this case, the result for both twins will be the same and the paternity cannot be determined. Therefore in such instances the DNA paternity test will not be of any help.
A recent case which was highly publicised in the media involved a pair of twins from Missouri that were identified as the possible fathers of a little girl. Both fathers denied the paternity and requested a DNA paternity test ? which of course could not distinguish the real father as they both had identical DNA. The court therefore had to decide based on the mother's testimony.
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