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 120, 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?
Approximately what percentage of the human genome codes for proteins?
Which human chromosome has been reported to have the most genes?
DNA fingerprinting is based on the variability found in which type of DNA sequences?
Which of the following is NOT a goal of the Human Genome Project?
In DNA fingerprinting, after restriction digestion and gel electrophoresis, the separated DNA fragments are transferred onto a membrane. This technique is called:
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?
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?
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, page 120. 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.) ---
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. 120F2 ratio in monohybrid cross — products of independent assortment of two alleles per locus.
| Symbol | Quantity | SI Unit |
|---|---|---|
| ratio | F2 progeny ratio | - |
F2 ratio in dihybrid cross with two independently-segregating loci, complete dominance, no linkage.
| Symbol | Quantity | SI Unit |
|---|---|---|
| ratio | F2 phenotype ratio | - |
In an idealised population (no mutation, drift, selection, gene flow, random mating), allele and genotype frequencies remain constant.
| Symbol | Quantity | SI Unit |
|---|---|---|
| p | freq of dominant allele A | - |
| q | freq of recessive allele a | - |
Proportion of recombinant offspring measures genetic distance between linked loci. Capped at 50% (independent assortment).
| Symbol | Quantity | SI Unit |
|---|---|---|
| RF | recombination frequency | % |
These are the exact patterns that cause wrong answers in NEET. Each trap includes when it triggers and how to avoid it.
Category: Sign Convention
DNA polymerase synthesises only 5'→3'. Leading strand: continuous, same direction as fork. Lagging: discontinuous (Okazaki), opposite to fork.
Question on Okazaki, leading vs lagging, primer direction.
Reading template 3'→5'; synthesising 5'→3'. Lagging strand needs short fragments because it can't run continuously against fork direction.
Category: Negative Marking
Five forces disturb HW: mutation, gene flow, drift, selection, non-random mating. ANY of these violates equilibrium.
Question asks which factor maintains/disturbs HW.
Random mating + no other forces → equilibrium. ANY of mutation/migration/drift/selection/assortative mating → disequilibrium.
Category: Similar Terms
Monohybrid: genotype 1:2:1 (AA:Aa:aa); phenotype 3:1.
Question asks for one ratio while presenting cross details.
Always note dominance: phenotype merges Aa + AA; genotype keeps them separate.
Category: Similar Terms
X-linked recessive (haemophilia, colour-blindness): affects males predominantly; carrier mother → 50% sons affected; affected father → all daughters carriers but not affected.
Pedigree question; carrier vs affected.
Sex chromosomes: XX vs XY. Recessive on X needs both copies (XaXa) in female, only one (XaY) in male.
Category: Similar Terms
Allopatric: geographic isolation. Sympatric: same area, no physical barrier (e.g. polyploidy in plants, host-shift).
Question gives speciation scenario and asks which type.
If geographic barrier mentioned → allopatric. If population overlaps → sympatric.
Root cause: formula misuse
Genotype frequencies: p² (AA) + 2pq (Aa) + q² (aa) = 1. Allele frequencies: p + q = 1. Don't drop 2pq.
Root cause: concept gap
ALL DNA pol synthesises 5'→3'. Lagging strand uses Okazaki fragments to APPEAR to extend toward fork while each fragment grows 5'→3'.
Root cause: concept gap
Frameshift = ANY indel NOT divisible by 3 (since codons are triplets). Indels of 3, 6, 9... preserve reading frame.
Root cause: term confusion
Start codon: AUG (Met / fMet). Stop codons: UAA (ochre), UAG (amber), UGA (opal/umber).
51 questions from NEET 2020, 2021, 2022, 2023, 2024, 2025. Answers verified against NTA official keys.
Identify the statement that is NOT correct.
Which factor is important for termination of transcription?
What is the pattern of inheritance for polygenic trait?
Which of the following statement is correct regarding the process of replication in E.coli?
Which one of the following factors will not affect the Hardy-Weinberg equilibrium?
The phenomenon of pleiotropism refers to
What is the role of RNA polymerase III in the process of transcription in Eukaryotes?
Among eukaryotes, replication of DNA takes place in :
Expressed Sequence Tags (ESTs) refers to
Unequivocal proof that DNA is the genetic material was first proposed by
Broad palm with single palm crease is visible in a person suffering from-
Select the correct group/set of Australian Marsupials exhibiting adaptive radiation.
XO type of sex determination can be found in :
The process of translation of mRNA to proteins begins as soon as :
Which of the following occurs due to the presence of autosome linked dominant trait ?
Detritivores breakdown detritus into smaller particles. This process is called:
If the length of a DNA molecule is 1.1 metres, what will be the approximate number of base pairs?
Which of the following is not a desirable feature of a cloning vector?
Mutations in plant cells can be induced by: 130. Match List-I with List-II.
Which of the following RNAs is not required for the synthesis of protein?
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Recurring question shapes from past papers. Each pattern shows why wrong options look tempting.
similar term confusion
Biology relies on precise terminology; close terms tempt selection.
Test yourself on this topic with real past-paper questions:
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