Revision: Genetics and Evolution >> Molecular Basis of Inheritance CUET (UG) Molecular Basis of Inheritance

The technique of identifying an individual by analyzing the unique DNA sequence present in each person, similar to fingerprints, is called DNA fingerprinting.

• The operon model, proposed by Jacob and Monod (1961), explains coordinated regulation of gene expression in prokaryotes at the transcriptional level.
• An operon consists of a promoter, operator, and a group of structural genes that are regulated together and transcribed as a single polycistronic mRNA.
• In the lac operon of E. coli, three structural genes—z (β-galactosidase), y (permease), and a (transacetylase)—are involved in lactose metabolism.
• The regulator gene (lac i) produces a repressor protein that binds to the operator and prevents transcription in the absence of lactose.
• When lactose is present, it inactivates the repressor, allowing RNA polymerase to transcribe the structural genes (induction).
• Catabolite repression occurs when glucose is present; lac operon expression is suppressed and later activated by CAP–cAMP when glucose is depleted.

• The Human Genome Project (HGP) was proposed in 1986 to map and sequence the entire human genome.
• It was an international effort involving about 100 laboratories from nearly 18 countries.
• The main goals included identifying all human genes, sequencing three billion base pairs, and storing data in databases.
• Two major approaches were used: Expressed Sequence Tags (ESTs) and whole genome sequencing with annotation.
• DNA fragments were cloned using BAC and YAC vectors in bacteria and yeast for sequencing.
• The human genome contains about 3.2 billion nucleotide bases and approximately 20,000–30,000 genes.
• Less than 2% of the genome codes for proteins, while repetitive DNA forms a large portion.
• About 99.9% of DNA sequences are identical among all humans; variations include SNPs and CNVs.
• HGP has applications in disease diagnosis, genetic counselling, gene therapy, and understanding human evolution.
• Ethical concerns include misuse of genetic data for discrimination, insurance denial, and attempts at genetic manipulation.

• DNA fingerprinting is a technique used to identify individuals based on unique patterns in their DNA sequences.
• It is based on repetitive DNA sequences called VNTRs (Variable Number Tandem Repeats), which show high polymorphism among individuals.
• These repetitive sequences are part of satellite DNA, including minisatellites and microsatellites.
• The technique was developed by Alec Jeffreys, and even a very small DNA sample can be used.
• The main steps include DNA extraction, PCR amplification, restriction digestion, gel electrophoresis, Southern blotting, hybridisation, and autoradiography.
• The resulting banding pattern is unique for each individual, except in identical (monozygotic) twins.
• DNA fingerprinting is widely used in forensic science, paternity testing, and personal identification.
• It is also useful in studying genetic diversity, population structure, and diagnosing certain inherited diseases.