Why is the Human Genome project is called a mega project?

The Human Genome Project (HGP) was called a mega project.

• It was an international effort formally begun in October 1990. The HGP was a 13 - year project coordinated by the U.S. Department of Energy and the National Institute of Health.
• The project was almost completed in 2003.

Need of the project:

• Knowledge about the effects of DNA variations among individuals leads to revolutionary new ways to diagnose, treat and someday prevent the thousands of disorders.
• HGP was closely associated with rapid development of Bioinformatics.
• It is used to understand the DNA sequences of non-human organisms besides human genome, to solve challenges in health care, agriculture, energy production, environmental remediation.

Goals of HGP:

• To identify all the (approximately 30,000) genes in human DNA.
• To determine the sequences of the 3 billion. chemical base pairs that make up human DNA.
• To improve tools for data analysis.
• To address the ethical, legal, and social issues (ELSI) that may arise from the project.

Methodologies:

• The methods involved two major approaches.
• One approach focused on identifying all the genes that expressed as RNA/referred to as Expressed Sequence Tags (ESTs).
• The other took the blind approach simply sequencing the whole set of genome that contained all the coding and non-coding sequence and later assigning different regions in the sequence with functions (a term referred to as Sequence Annotation).
• DNA sequencing: DNA sequencing is the process of determining the exact order of three billion base pairs.
• The DNA fragments were sequenced using automated DNA sequencers that worked on a method developed by Frederick Sanger.
• Shotgun sequencing is the latest method of sequencing even for longer fragments.

Salient Features of Human Genome:

• The human genome contains 3billion nucleotide bases.
• On average a gene consists of 3000 bases. The largest known human gene codes for the protein called dystrophin.
• The total number of genes is estimated at 30,000. Almost 99.9% nucleotide bases are same in all people.
• The functions are unknown for over 50% of the discovered genes.
• Less than 2% of genome codes for proteins.
• Repeated sequences make up very large portion of the human genome.
• Repetitive sequences are stretches of DNA sequences that are repeated many times. They are thought to have no direct coding functions, but they shed light on chromosome structure, dynamics and evolution.
• Chromosome 1 has the highest number of genes 2,968 and Y-Chromosome has fewest genes 231.

Advantages of HGP:

• Identification and mapping of the genes responsible for genetic diseases helps in diagnosis, treatment and prevention of these diseases.
• Detailed knowledge of the genomes of humans and other species will give a clear picture of
  gene expression.
• Earlier detection of genetic predispositions to disease, rational drug design, gene therapy is
  going to be easy with more knowledge on human genome. 
• A new era of Molecular Medicine looking into the most fundamental causes of diseases then treating the symptoms will be an important advantage. 

Due to all the above features, the HGP is called mega project.