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Paternity Diagnosis

• Paternity Diagnosis helps to establish genetic proof whether a man is the biological father of an individual or not. This paternity test is carried out by using DNA analysis.  The DNA analysis through DNA fingerprinting offers a more reliable way to determine the genetic parent. Before DNA fingerprinting came into existence, blood group polymorphisms like ABO, MN and Rh systems were most widely used.  But using these blood group polymorphisms, a particular person can be excluded as the parent of a child.  The exclusion of parentage can be determined with certainty.
• But to determine parentage, DNA analysis is the most advanced and accurate technology. This paternity test compares a child’s DNA pattern with that of the alleged father to check for evidence of this inheritance.  The DNA fingerprinting technique assures the probability of parents to more than 99.9% if the alleged father is biologically related and the probability is 0% when the alleged father is not biologically related to the child.

Now let us briefly familiarise ourselves with the structure of DNA:

• DNA: DNA (Deoxyribonucleic acid) is a chemical structure that forms chromosomes. A piece of a chromosome that dictates a particular trait is called a gene. The structure of the DNA molecule was proposed by James Watson and Francis Crick in 1953.  DNA is a polymer (a large molecule containing repeated units) composed of a sugar, phosphoric acid and four nitrogen bases.  Two of these nitrogen bases are purines, the other two are pyramidines.  The purines bases are adenine (A) and guanine (G) and the pyramidine bases are thymine (T) and cytosine (C). The two strands of DNA are connected at each base. Each base will only bond with one other base, as follows: Adenine (A) will only bond with thymine (T), and guanine (G) will only bond with cytosine (C).  The structure of DNA is presented below in Fig.4.1.
  DNA Structure
• DNA Finger Printing: This is also known as DNA typing or Genetic Fingerprinting.
  After knowing the DNA structure, we now briefly familiarise ourselves with the procedure adopted in DNA finger printing: 
  DNA samples can be extracted from blood, semen, hair roots, bone or saliva. The extracted DNA is then treated with restriction enzymes, which cuts the DNA into smaller fragments by cutting at specific sites. This DNA is then amplified by the technique of Polymerase chain reaction (PCR). By using alkaline chemicals this double stranded DNA splits into single stranded DNA. The DNA fragments are then subjected to agarose gel electrophoresis. The DNA bands so formed are transferred to nylon membrane. This is treated with a radioactively-labelled DNA probe which binds to complemental DNA sequences on the membrane. The excess DNA probe is then washed off. The radioactive DNA pattern is transferred to X-ray film by direct exposure. When developed, the resultant pattern is the DNA fingerprint.