Question

What is it that 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.

Answer 1

Answer: (D)

DNA fingerprinting is a technique of determining nucleotide sequences of certain areas of DNA which are unique to each individual. The difference of about 0.1% or $3 \times 10^6$ base pairs (out of $3 \times 10^9$ bp) provides individuality to each human being. Human genome possesses numerous small noncoding but inheritable sequences of bases which are repeated many times. These sequences occur near telomere, centromeres, Y chromosome and heterochromatic area. The area with same sequence of bases repeated several times is called repetitive DNA. It is separated as satellite from the bulk DNA during density gradient centrifugation and hence called satellite DNA where, repetition of bases is in tandem. Satellite DNAs show polymorphism (the occurrence of mutations in a population at high frequency), which is the basis of genetic mapping of human genome as well as DNA fingerprinting. While mutations in genes produce alleles with different expressions, mutations in noncoding repetitive DNA have no immediate impact. These mutations which have piled up with time form the basis of polymorphism.