Here is a trap that costs marks on this topic: confusing the goals and methodology of the Human Genome Project with DNA fingerprinting, or mixing up their key numerical facts.
Human Genome Project (HGP) was a 13-year international effort (1990–2003) coordinated by the US Department of Energy and the National Institutes of Health. The goal was to sequence all approximately 3.2 billion base pairs of the human genome and identify all genes (estimated ~20,000–25,000). NCERT Class 12 Biology Chapter 5 (Molecular Basis of Inheritance), page 104, covers HGP's salient features: only ~2% of the genome codes for proteins; repetitive sequences make up a large portion; the average gene size is about 3,000 bases; chromosome 1 has the most genes, Y chromosome the fewest.
DNA fingerprinting exploits the variability in repetitive DNA sequences (VNTRs — Variable Number Tandem Repeats, or STRs — Short Tandem Repeats) between individuals. The technique, developed by Alec Jeffreys, involves restriction digestion, gel electrophoresis, Southern blotting, and hybridisation with labelled VNTR probes to produce a unique banding pattern. It is used in forensic identification, paternity disputes, and evolutionary studies.
Where NEET catches you: Questions test precise recall — the number of base pairs in the human genome, which chromosome has the most/fewest genes, the percentage of coding DNA, the year HGP completed, and the principle underlying DNA fingerprinting (polymorphism in repetitive sequences, NOT coding sequences). The common confusion is stating that DNA fingerprinting analyses coding gene sequences; it does not — it targets non-coding repetitive DNA.
Watch out for stems that ask "the basis of DNA fingerprinting" — the answer is polymorphism in repetitive (satellite) DNA, not SNPs in coding regions.
Select an option to see the explanation. Wrong answers show why your choice was tempting — and name the exact trap it exploits.
The Human Genome Project was completed in which year?
Answer: D. The HGP was completed in 2003 after 13 years of work (launched 1990). NCERT Class 12 Biology Chapter 5, page 102.
Why A is wrong: A is wrong because 2000 was the year the draft sequence was announced, not the final completion.
Why B is wrong: B is wrong because 2001 saw the publication of the draft sequence analysis, not project completion.
Why C is wrong: C is wrong because the project concluded in 2003; 2005 has no specific HGP milestone.
Approximately what percentage of the human genome codes for proteins?
Answer: A. Less than 2% of the human genome is coding sequence. The vast majority is non-coding, including repetitive sequences and introns. NCERT Class 12 Biology Chapter 5, page 104.
Why B is wrong: B is wrong because 10% is a significant overestimate; the actual coding fraction is far smaller.
Why C is wrong: C is wrong because one-quarter of the genome coding for proteins would be a gross overestimate of the ~2% figure.
Why D is wrong: D is wrong because half the genome coding for proteins contradicts HGP findings; most DNA is non-coding.
Which human chromosome has been reported to have the most genes?
Answer: C. Chromosome 1 has the most genes among all human chromosomes. NCERT Class 12 Biology Chapter 5, pages 103–104.
Why A is wrong: A is wrong because the X chromosome, while large, does not carry the most genes — chromosome 1 does.
Why B is wrong: B is wrong because chromosome 22 was the first to be fully sequenced but does not have the most genes.
Why D is wrong: D is wrong because chromosome 21 is one of the smallest human autosomes and carries fewer genes.
DNA fingerprinting is based on the variability found in which type of DNA sequences?
Answer: D. DNA fingerprinting exploits polymorphism in non-coding repetitive DNA (VNTRs/STRs), which show high variability between individuals. NCERT Class 12 Biology Chapter 5, pages 105–106. The principle requires applying the concept that it is non-coding repeats — not coding genes — that provide individual-specific banding patterns.
Why A is wrong: A is wrong because coding sequences are relatively conserved between individuals and are NOT the basis of DNA fingerprinting. This is a common confusion — fingerprinting targets non-coding repetitive DNA.
Why B is wrong: B is wrong because mitochondrial coding sequences, while useful in some evolutionary studies, are not the basis of the VNTR-based DNA fingerprinting technique described in NCERT.
Why C is wrong: C is wrong because rRNA genes are highly conserved across species (needed for translation) and show little inter-individual variation.
Which of the following is NOT a goal of the Human Genome Project?
Answer: A. The HGP aimed to sequence the genome, identify genes, store information in databases, develop analytical tools, and address ethical/legal/social issues. Developing gene therapy protocols was not a stated goal of HGP. NCERT Class 12 Biology Chapter 5, page 102. This requires applying knowledge of HGP's stated objectives to identify the incorrect claim.
Why B is wrong: B is wrong because identifying all estimated genes (~20,000–25,000) was indeed a core HGP objective.
Why C is wrong: C is wrong because sequencing all ~3.2 billion base pairs was the primary goal of HGP.
Why D is wrong: D is wrong because creating databases for genomic data storage and sharing was an explicit HGP goal (e.g., GenBank).
In DNA fingerprinting, after restriction digestion and gel electrophoresis, the separated DNA fragments are transferred onto a membrane. This technique is called:
Answer: C. Southern blotting (named after Edwin Southern) is used to transfer DNA fragments from an agarose gel to a nitrocellulose or nylon membrane for hybridisation with probes. NCERT Class 12 Biology Chapter 5, page 106. This requires applying knowledge of the DNA fingerprinting protocol steps.
Why A is wrong: A is wrong because Northern blotting is used for RNA, not DNA. The naming follows a directional pun tradition but the techniques differ by target molecule.
Why B is wrong: B is wrong because Western blotting detects proteins using antibodies, not DNA fragments.
Why D is wrong: D is wrong because 'Eastern blotting' is not a standard, widely recognised molecular biology technique in NCERT.
A student claims that since the Human Genome Project sequenced all human DNA, every individual's genome is now known. What is the flaw in this reasoning?
Answer: B. HGP produced a composite reference genome from a few donor individuals, not a personalised sequence for every human. Individual variation (SNPs, VNTRs) means each person's genome differs. This requires applying the concept of genomic variation to evaluate the student's claim. NCERT Class 12 Biology Chapter 5, page 105.
Why A is wrong: A is wrong because HGP sequenced the entire genome (coding and non-coding), not just coding regions.
Why C is wrong: C is wrong because HGP focused on nuclear DNA (all chromosomes); mitochondrial DNA had already been sequenced earlier.
Why D is wrong: D is wrong because HGP included all 22 autosomes plus the X and Y sex chromosomes.
In a forensic investigation, DNA fingerprinting of a crime scene sample and four suspects gave the following VNTR banding patterns. The crime scene sample shows bands at positions 2, 5, and 8. Suspect A shows bands at 2, 5, 8; Suspect B at 1, 5, 8; Suspect C at 2, 5, 7; Suspect D at 3, 5, 9. Which suspect's DNA matches the crime scene sample?
Answer: B. DNA fingerprinting requires an exact match of ALL banding positions. Suspect A shows bands at 2, 5, and 8 — identical to the crime scene sample. This requires two linked reasoning steps: (1) understanding that all bands must match for a positive identification, and (2) systematically comparing each suspect's pattern to the evidence. NCERT Class 12 Biology Chapter 5, pages 106–107.
Why A is wrong: A is wrong because Suspect B differs at position 1 (crime scene has band 2, not 1). Even a single band mismatch rules out a match.
Why C is wrong: C is wrong because Suspect C differs at position 7 (crime scene has band 8, not 7). Partial matches are not sufficient for forensic identification.
Why D is wrong: D is wrong because Suspect D differs at two positions (3 instead of 2, and 9 instead of 8). This is clearly a non-match.
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Given
A forensic lab receives a blood sample from a crime scene. DNA is extracted and subjected to restriction enzyme digestion. After gel electrophoresis and Southern blotting, hybridisation with a VNTR probe reveals bands at 4 different positions. Five suspects are tested. Suspect X shows bands at all 4 matching positions plus one additional band.
Required
Can Suspect X be identified as the source of the crime scene DNA?
Concept
DNA fingerprinting compares VNTR banding patterns. A match requires that every band in the evidence sample is present in the suspect's profile. The principle is based on polymorphism in repetitive (satellite) DNA, per NCERT Class 12 Biology Chapter 5, pages 105–106. This connects to PYQ pattern NEET pattern: unit bundle, which tests recall and direct application of DNA fingerprinting principles.
Formula / Rule
For a positive match: every band in the evidence profile must appear in the suspect's profile. Additional bands in the suspect's profile do not exclude a match (the crime scene sample may be a partial profile due to degradation).
Substitution
Evidence bands: positions A, B, C, D (4 bands).
Suspect X bands: positions A, B, C, D, E (5 bands — all 4 evidence bands present plus one extra).
Calculation / Reasoning
Step (i): Check if all evidence bands are present in suspect → A ✓, B ✓, C ✓, D ✓.
Step (ii): The extra band (E) in Suspect X could mean the crime scene sample was partially degraded (lost one band) or that the suspect has heterozygous VNTR alleles producing an extra band at that locus. The key criterion is that all evidence bands must be accounted for — they are.
Final answer
Suspect X cannot be excluded as the source. All evidence bands match. However, a definitive forensic conclusion would require statistical analysis of band frequencies in the population to calculate the probability of a random match. In a NEET context, if all bands match, the suspect is identified as the match.
Common trap
Students often think an extra band in the suspect's profile means "no match." This is incorrect — the crime scene DNA may be degraded. The critical check is whether ALL evidence bands appear in the suspect, not whether the suspect has ONLY those bands. Another common confusion: stating that DNA fingerprinting analyses coding gene sequences. It does not — it targets non-coding repetitive (satellite) DNA.
Similar NEET-style question
"In a paternity dispute, the child shows VNTR bands at positions 1, 3, 5, and 7. The mother shows bands at 1, 3, 6, and 9. Which bands in the child must have come from the biological father?" (Answer: bands at positions 5 and 7, since bands 1 and 3 could be maternal.)
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Human Genome Project (1990-2003): ~3 billion bp; ~20,000-25,000 genes. DNA fingerprinting: VNTRs (variable number tandem repeats); RFLP analysis; PCR amplification; gel electrophoresis. Used in forensics, paternity.
-- NCERT Class 12 Biology, Ch. 5, p. 102More in Genetics and Evolution: 21 exam traps and mistakes · 4 formulas · 1 question pattern from its other lessons.
4 questions from NEET 2021, 2022, 2023, 2025. Answers verified against NTA official keys.
Which chromosome in the human genome has the highest number of genes?
Expressed Sequence Tags (ESTs) refers to
Page numbers are the ones printed in the current NCERT textbook (2023 rationalised edition), unless marked pre-2023. The books are free at ncert.nic.in.
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