'There is a paternity dispute for a child'. Which technique can solve the problem? Discuss the principle involved.

(A) $DNA$ fingerprinting is used to solve paternity disputes. $DNA$ fingerprinting involves identifying differences in specific regions of $DNA$ sequences called repetitive $DNA$,where a small stretch of $DNA$ is repeated many times.
These repetitive $DNA$ sequences are separated from bulk genomic $DNA$ as different peaks during density gradient centrifugation. The bulk $DNA$ forms a major peak,while smaller peaks are referred to as satellite $DNA$. Depending on base composition ($A:T$ rich or $G:C$ rich),length of the segment,and the number of repetitive units,satellite $DNA$ is classified into categories like micro-satellites and mini-satellites. These sequences generally do not code for proteins but constitute a large portion of the human genome.
These sequences show a high degree of polymorphism,which forms the basis of $DNA$ fingerprinting. Since $DNA$ from any tissue (blood,hair follicle,skin,bone,saliva,sperm,etc.) of an individual shows the same degree of polymorphism,it is a powerful identification tool in forensic applications. Furthermore,because these polymorphisms are inheritable from parents to children,$DNA$ fingerprinting is the basis for paternity testing.
The technique was developed by Alec Jeffreys. In India,Lalji Singh is known as the father of $DNA$ fingerprinting. He used a satellite $DNA$ probe showing high polymorphism,known as Variable Number of Tandem Repeats $(VNTR)$.
The technique involves Southern blot hybridization using radiolabeled $VNTR$ as a probe,consisting of the following steps:
$(i)$ Isolation of $DNA$,
$(ii)$ Digestion of $DNA$ by restriction endonucleases,
$(iii)$ Separation of $DNA$ fragments by electrophoresis,
$(iv)$ Transferring (blotting) of separated $DNA$ fragments to synthetic membranes (nitrocellulose or nylon),
$(v)$ Hybridization using a labeled $VNTR$ probe,and
$(vi)$ Detection of hybridized $DNA$ fragments by autoradiography.