DNA Structure & RNA Function—NEET Biology

Correct answer: A — S1 and S4 only

The core concept here is the molecular basis of uniqueness in DNA fingerprinting, specifically the role of Variable Number of Tandem Repeats (VNTRs). S1: VNTRs are indeed non-coding, highly polymorphic repetitive DNA sequences and form the basis of DNA fingerprinting. This statement is correct, as per NCERT Section 5.10, which states, 'These sequence show high degree of polymorphism and form the basis of DNA fingerprinting.' S2: The copy number of VNTRs varies not only between individuals but also from chromosome to chromosome within a single individual. Thus, the statement that the copy number is consistent across all chromosomes within an individual is incorrect. NCERT states, 'The copy number varies from chromosome to chromosome in an individual.' S3: DNA fingerprinting generally cannot distinguish between monozygotic (identical) twins because they originate from a single zygote and therefore have virtually identical DNA sequences, including VNTR patterns. NCERT explicitly states, 'It differs from individual to individual in a population except in the case of monozygotic (identical) twins.' This statement is incorrect. S4: Polymorphism in VNTRs is characterized by variations in the number of tandem repeat units, which consequently leads to variations in the overall length of the DNA fragment containing the VNTR. These length variations result in bands of differing sizes in autoradiography. This statement is correct. NCERT mentions, 'The numbers of repeat show very high degree of polymorphism. As a result the size of VNTR varies in size from 0.1 to 20 kb. Consequently, after hybridisation with VNTR probe, the autoradiogram gives many bands of differing sizes.' S5: VNTRs belong to a class of satellite DNA referred to as mini-satellites, not micro-satellites. Furthermore, repetitive DNA, including VNTRs, are separated from bulk genomic DNA as different (small) peaks during density gradient centrifugation, while the bulk DNA forms a major peak. This statement is incorrect. NCERT states, 'The VNTR belongs to a class of satellite DNA referred to as mini-satellite.' and '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.' Therefore, only statements S1 and S4 are correct. The tested concept is the properties of VNTRs and their application in DNA fingerprinting.