Paternity dispute has always posed a challenge in the past; over the decades the biological science world has tried with different types of tests to solve it. As far back as the 1920s attempts at solving this painful ordeal was made using blood group. There are basically four different types of blood groups in the human population; A, B, AB and O. These groups are genetically inherited and could be used to show relationship between a child and the parents. Its main pit fall was that it could not exclude other members of the population. Its invaluable use today is in cross matching blood for compatibility during transfusion.
A decade later, following the discovery of other forms of inherited blood antigens like Duffy, Kelly and the Rhesus factor, attempts at resolving paternity dispute was switched to test with these antigens on red blood cells. This also had the same draw back as that of the ABO blood group system in terms of accuracy. Not all members of the population could be excluded in the test. However these days, the Rhesus factor is still very important in blood transfusion and iso- immunization challenge during pregnancy.
A greater stride was made in the 1970s with the discovery of HUMAN LEUKOCYTE ANTIGEN (HLA). This protein which is abundant in white blood cells is surprisingly not found in oxygen carrying red blood cells. The protein can be found in almost all other cells of the body and has the added advantage that it varies from one individual to another. Because of this high variability, it gave a very high index of exclusion and made it a powerful immunological test in paternity dispute. In spite of this, HLA testing is not an ideal technique because it requires large sample of blood that must be fresh because of the short life span of white blood cells .On the other hand collecting blood from infants below the age of five years because of the volume required could be dangerous. All said HLA is very useful in the issue of compatibility when it comes to organ transplant.
During reproduction the male sperm contains half of the genetic materials present in the cells of the body while the female egg contains same. When they fuse, they form a zygote which has the complement of the DNA from both parents. This zygote would undergo multiple division, multiplications and differentiation into the various organ systems that would become human. The import of this is that all cells in the body so long as it has a nucleus would have the same genetic and DNA composition.
The DNA testing revolution actually started in 1953 following the work of Rosalind Franklin, Maurice Wilkins and Ray Gosling. They had used X-ray diffraction to unravel the helical ladder shaped structure of the DNA. Since then the exploits in DNA engineering has grown in leaps and bounds. The first technique applied in paternity dispute resolution is the RESTRICTION FRAGMENT LENGTH POLYMORPHISM (RFLP). In this process, unique sections of the DNA are sliced. These sections from the parents are then compared with those of the child. As a rule, half of the child’s DNA should match that of the mother and the other half that of the father’s if there is a biological relationship.
Occasionally, the child’s DNA may not match that of either parent. This is usually caused by GENETIC MUTATION; which is the spontaneous alteration in the base sequence of a particular gene due to error in DNA duplication or damage.
When this does happen, statistical analysis to determine the possibility of genetic mutation and biological relationship between family members is carried out. This procedure gives very high accuracy but has a major drawback in the sense that large sample of blood is required and the procedure is time consuming.
The revolution in paternity dispute resolution with DNA using POLYMERASE CHAIN REACTION technique was actually started in 1956 following the discovery of the enzyme DNA POLYMERASE in the bacteria Escherichia Coli, E Coli for short by Arthur Kornberg. The main function of this enzyme is to make copies of DNA from nucleotides which are the building blocks. The striking feature of DNA polymerase is that it has a very rigid structure and there is hardly any difference or variation in the catalytic subunits between species. It is basically the same in all species that it is found. Interestingly DNA polymerase cannot begin a new chain of DNA but can only add nucleotides to pre existing DNA.
The polymerase chain reaction, which was developed by KayMullis, involves heating and cooling of samples that eventually leads to DNA melting. This essentially involves the breaking of the Hydrogen bonds. Here the DNA polymerase enzymatically assembles a new DNA strand from nucleotides using the previous split single stranded one as a template. This cycle is repeated and DNAs are produced in geometric manner leading to millions and billions of copies in very short period not more than a couple of minutes. The speed with which results are obtained makes polymerase chain reaction the current ultimate procedure in genetic engineering.
In practice; with regards to paternity dispute swab samples are collected from the buccal (mouth) cavities of the mother, child and the alleged father. These samples are now subjected to PCR procedure.After amplification the three samples are now compared for similarity. Where there is a biological relationship the result from this test is 100 per cent accurate. The fact is; for there to be life the DNA or chromosomes of the child must contain those of both parents. Again during polymerase chain reaction, no new DNA is created. It is only the ones present that are amplified.
The beauty in it all is that samples required for the test is small and the process of collection is not cumbersome or traumatic. In terms of procedure; after sample collection and necessary substrates especially the nucleotides, the polymerase enzyme and a buffer solution, what basically is involved is variation of the temperature that would make the various steps in the synthesis of the DNAs easy. Simply put, it involves heating and cooling without the temperature ever getting to the boiling point of water. This process is often referred to as thermo cycling using a thermoelectric device.
This procedure has made the challenge of paternity dispute almost a tea party. The result is indisputable because of its accuracy and accepted in the law courts in countries that has made it commonplace. In our environment the cost and emotional upset may factor in. That notwithstanding, when next you are not very sure, don’t go about denying because you feel that may be the easy way out; because with DNA testing, you might just be the one who done it!
I wish you all the best and happy weekend.