Human Genome Project and DNA fingerprinting

The essentials

The Human Genome Project (HGP) was launched in 1990 and completed in 2003. It was a mega project, coordinated by the U.S. Department of Energy and the National Institutes of Health, with contributions from several countries. Goals included identifying all the genes in human DNA, determining the sequences of the 3 billion chemical base pairs, storing the information in databases, improving tools for data analysis, transferring technologies to other sectors, and addressing the ethical, legal and social issues (ELSI).

Methods: one approach (Expressed Sequence Tags, ESTs) focused on identifying genes expressed as RNA; another (sequence annotation) sequenced the whole genome, both coding and non-coding, and later assigned functions. DNA was broken into fragments and cloned in hosts using vectors such as BAC (bacterial artificial chromosomes) and YAC (yeast artificial chromosomes). Automated sequencers based on Frederick Sanger's method were used.

Salient findings:

• The human genome has about 3164.7 million bp.
• The average gene has about 3000 bases; the largest known human gene, dystrophin, has 2.4 million bases.
• The HGP estimated the total number of genes at about 30,000 (the NCERT figure; later estimates are lower, around 20,000).
• 99.9% of nucleotide bases are the same in all people.
• Less than 2% of the genome codes for proteins; repeated sequences make up a large part.
• Chromosome 1 has the most genes (2968) and the Y chromosome the fewest (231).
• About 1.4 million locations of single-base DNA differences (SNPs) were identified.

DNA fingerprinting compares differences in repetitive DNA, in which a short sequence is repeated many times. Polymorphism means variation at the genetic level that occurs with a frequency of more than 0.01 in a population. Alec Jeffreys used a satellite DNA probe called VNTR (variable number of tandem repeats); the number of repeats varies between individuals. Steps: isolate DNA, digest with restriction enzymes, separate fragments by electrophoresis, transfer to a membrane (Southern blotting), hybridise with a labelled VNTR probe and detect by autoradiography. It is used in forensics, paternity disputes and population studies.