The correct option is A Polymorphism in DNA sequence
The basis of genetic mapping of the human genome as well as of DNA fingerprinting is polymorphism in DNA sequence.
DNA Polymorphism is the genetic variation in different individuals of the same species in a population. It is due to these variations that every individual has unique DNA sequences.
There are a number of different DNA polymorphisms such as satellite DNA, SNP, etc.
Satellite DNA: These are highly repetitive stretches of DNA present on chromosomal ends and centromeres. A single sequence of nucleotides is repeated many times one after the other tandemly. They show a high degree of polymorphism.
Variable number of tandem repeats (VNTR) is a mini satellite which usually has unit repeat size of about 10 - 100 bp.
VNTRs are used in DNA fingerprinting. DNA fingerprinting is a laboratory technique which relies on the repetitive sequences of DNA of a person to determine his/ her unique identity.
SNP: SNP stands for single nucleotide polymorphism which is a genetic variation due to a single nucleotide difference in the DNA.
Hence, the option a is correct.