Q. Which of the following forms the basis of DNA fingerprinting?
(a) The relative proportions of purines and pyrimidines in DNA.
(b) The relative difference in the DNA occurrence in blood, skin and saliva.
(c) The relative amount of DNA in the ridges and grooves of the fingerprints.
(d) Satellite DNA occurring as highly repeated short DNA segments.
Solution :
Correct option : D DNA fingerprinting involves identifying differences in some specific regions in DNA sequence called as repetitive DNA, because in these sequences, a small stretch of DNA is repeated many times. These repetitive DNA are separated from bulk genomic DNA as different peaks during density gradient centrifugation. The bulk DNA forms a major peak and the other small peaks are referred to as satellite DNA. Depending on base composition (A:T rich or G:C rich), the length of the segment, and a number of repetitive units, the satellite DNA is classified into many categories, such as micro-satellites, mini-satellites, etc. These sequences normally do not code for any proteins, but they form a large portion of the human genome. These sequences show a high degree of polymorphism and form the basis of DNA fingerprinting. Since, DNA from every tissue (such as blood, hair follicle, skin, bone, saliva, sperm, etc.), from an individual, show the same degree of polymorphism, they become very useful identification tool in forensic applications.