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The last two sections of NCERT's Molecular Basis of Inheritance chapter are packed with numbers and steps: base pairs, gene counts, SNPs, VNTRs, Southern blotting. Questions on them are often direct, which makes them easy marks if you have the facts straight and costly if you mix them up. This post organises what NCERT says, works two calculations, and lists the traps.
Where does this sit in the syllabus?
The NEET (UG) 2026 syllabus lists "Genome and human genome project; DNA finger printing" in the genetics unit. Both topics are in NCERT Class 12 Biology, Chapter 5, sections 5.9 and 5.10. CBSE Class 12 students meet the same sections. Check the syllabus for your exam year.
What did the Human Genome Project set out to do?
NCERT describes the HGP as a "mega project" launched in 1990. It was a 13-year project coordinated by the U.S. Department of Energy and the National Institutes of Health, with the Wellcome Trust (UK) as a major partner and contributions from Japan, France, Germany, China and others. It was completed in 2003.
Its goals, as NCERT lists them, included identifying all the approximately 20,000–25,000 genes, determining the sequence of the 3 billion base pairs, storing the information in databases, improving tools for analysis, transferring technology to other sectors, and addressing ethical, legal and social issues (ELSI).
Methods to remember:
Two approaches. Expressed Sequence Tags (ESTs) focused on genes expressed as RNA. Sequence annotation sequenced the whole genome first and assigned functions later.
Cloning hosts and vectors. Bacteria and yeast, with BACs (bacterial artificial chromosomes) and YACs (yeast artificial chromosomes).
Sequencing. Automated sequencers based on Frederick Sanger's method, with computer programs to align overlapping fragments.
The last chromosome. Chromosome 1 was completed only in May 2006.
What did the HGP find?
NCERT's list of salient features is a favourite source of one-line questions:
The genome has 3164.7 million bp.
The average gene has 3000 bases; the largest known human gene, dystrophin, has 2.4 million.
About 30,000 genes, far fewer than earlier estimates of 80,000 to 1,40,000.
99.9% of nucleotide bases are the same in all humans.
Functions are unknown for over 50% of discovered genes.
Less than 2% of the genome codes for proteins.
Chromosome 1 has the most genes (2968); Y has the fewest (231).
About 1.4 million single-base differences (SNPs) were identified.
Note that NCERT gives two gene figures: 20,000–25,000 in the goals and about 30,000 in the findings. Read which one the question is about.
The story did not end in 2003. The U.S. National Human Genome Research Institute's HGP fact sheet says the April 2003 sequence covered about 92% of the genome with fewer than 400 gaps, and that the Telomere-to-Telomere consortium announced the first truly complete sequence on 31 March 2022. The paper by Nurk and colleagues (2022) describes that 3.055 billion base pair sequence. For your exam, use NCERT's figures.
How does DNA fingerprinting work?
Since 99.9% of the sequence is shared, fingerprinting looks at the parts that vary most: repetitive DNA, where short stretches repeat many times. In density gradient centrifugation these separate from bulk DNA as small peaks called satellite DNA, classed as micro-satellites, mini-satellites and so on. They usually do not code for proteins but show a high degree of polymorphism.
Alec Jeffreys developed the technique using a probe for a satellite DNA called VNTR (Variable Number of Tandem Repeats), a mini-satellite. His work appeared in Nature in 1985 as Individual-specific 'fingerprints' of human DNA. NCERT lists six steps:
Isolation of DNA.
Digestion with restriction endonucleases.
Separation of fragments by electrophoresis.
Blotting onto nitrocellulose or nylon membranes.
Hybridisation with a labelled VNTR probe.
Detection by autoradiography.
VNTRs range from 0.1 to 20 kb, so the autoradiogram shows many bands of different sizes, a pattern unique to each person except identical twins. PCR has made the method sensitive enough to work from a single cell.
Worked examples
1. How many bases differ between two people? NCERT asks this directly. If 99.9% is the same, 0.1% differs: 0.001 × 3 × 10⁹ = 3 × 10⁶ base pairs.
2. Paternity bands. A child's fingerprint shows bands P, Q, R and S. The mother has bands P and R. Each band in a child must come from one parent, so the biological father must carry Q and S. A man who lacks either band can be excluded.
NCERT's book example is worth one more line: at 1000 letters a page and 1000 pages a book, 3.3 × 10⁹ bp would fill 3.3 × 10⁹ / 10⁶ = 3300 books.
Common traps
VNTR is a mini-satellite, not a micro-satellite.
Southern blotting is part of classic fingerprinting; Sanger's method was used for sequencing in the HGP. Do not swap them.
Satellite DNA separates in density gradient centrifugation, not electrophoresis.
Identical twins are the one case where fingerprints match.
A polymorphism is a variant present at a frequency above 0.01 in the population.
For the rest of the chapter, see our guide to the molecular basis of inheritance, and for restriction enzymes and electrophoresis, biotechnology principles. If one step, such as why the probe binds only certain bands, still does not make sense, the Fermi Concept Library covers every concept in biology with its own lesson, so you can fix that one idea.
Close your book now and write the six fingerprinting steps and five HGP findings from memory, then check them against NCERT.
