Read the passage given below and answer the questions that follow.
DNA fingerprinting involves identifying differences in some specific regions in DNA sequence called repetitive DNA, because in these sequences, a small stretch of DNA is repeated many times. 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. Polymorphism (variation at genetic level) arises due to mutations. New mutations may arise in an individual either in somatic cells or in the germ cells (cells that generate gametes in sexually reproducing organisms). If a germ cell mutation does not seriously impair the individual’s ability to have offspring who can transmit the mutation, it can spread to the other members of the population (through sexual reproduction). The technique of DNA fingerprinting was initially developed by Alec Jeffreys. He used a satellite DNA as probe that shows a very high degree of polymorphism. It was called Variable Number of Tandem Repeats (VNTR).
Match List-I with List-II.
| List-I | List-II |
| (A) DNA from every tissue of an individual shows the same degree of polymorphism | (I) Basis of paternity testing, in case of disputes |
| (B) Polymorphisms are inheritable from parents to children | (II) Promises to revolutionise finding chromosomal locations for disease-associated sequences |
| (C) Use of polymerase chain reaction (PCR) | (III) Very useful identification tool in forensic applications |
| (D) Single nucleotide polymorphism (SNP) locations identified in humans | (IV) DNA from a single cell is enough to perform DNA fingerprinting analysis |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → A-III, B-I, C-IV, D-II
(A) DNA from every tissue of an individual shows the same degree of polymorphism — this matches (III) Very useful identification tool in forensic applications. Blood, hair follicle, skin, bone, saliva or sperm left at a crime scene all give the same fingerprint as that person’s blood sample. So any tissue found can be matched to a person.
(B) Polymorphisms are inheritable from parents to children — this matches (I) Basis of paternity testing, in case of disputes. A child receives one allele of each chromosome from each parent. Every band in the child’s fingerprint must come from the mother or the true father, so the father can be identified.
(C) Use of polymerase chain reaction (PCR) — this matches (IV) DNA from a single cell is enough to perform DNA fingerprinting analysis. PCR makes many copies of a DNA segment. It has increased the sensitivity of the technique so much that a very tiny sample is enough.
(D) Single nucleotide polymorphism (SNP) locations identified in humans — this matches (II) Promises to revolutionise finding chromosomal locations for disease-associated sequences. SNPs are single-base DNA differences between people. Scientists have identified about 1.4 million such locations in humans, and they also help in tracing human history.
NCERT Extract:
DNA Fingerprinting – “… These sequence show 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. Further, as the polymorphisms are inheritable from parents to children, DNA fingerprinting is the basis of paternity testing, in case of disputes.”
DNA Fingerprinting – “… The sensitivity of the technique has been increased by use of polymerase chain reaction (PCR– you will study about it in Chapter 9). Consequently, DNA from a single cell is enough to perform DNA fingerprinting analysis.”
Salient Features of Human Genome – “… (ix) Scientists have identified about 1.4 million locations where single-base DNA differences (SNPs – single nucleotide polymorphism, pronounced as ‘snips’) occur in humans. This information promises to revolutionise the processes of finding chromosomal locations for disease-associated sequences and tracing human history.”