Human Genome Project: In the preceding sections you have learnt that it is the sequence of bases in DNA that determines the genetic information of a given organism. In other words, genetic make-up of an organism or an individual lies in the DNA sequences. If two individuals differ, then their DNA sequences should also be different, at least at some places.

These assumptions led to the quest of finding out the complete DNA sequence of human genome. With the establishment of genetic engineering techniques where it was possible to isolate and clone any piece of DNA and availability of simple and fast techniques for determining DNA sequences, a very ambitious project of sequencing human genome was launched in the year 1990. Human Genome Project (HGP) was called a mega project.

Goals of Human Genome Project

• Identify all the approximately 20,000-25,000 genes in human DNA;
• Determine the sequences of the 3 billion chemical base pairs that make up human DNA;
• Store this information in databases;
• Improve tools for data analysis;
• Transfer related technologies to other sectors, such as industries;
• Address the ethical, legal, and social issues (ELSI) that may arise from the project.

Salient Features of Human Genome Project

• The human genome contains 3164.7 million bp.
• The average gene consists of 3000 bases, but sizes vary greatly, with the largest known human gene being dystrophin at 2.4 million bases.
• The total number of genes is estimated at 30,000–much lower than previous estimates of 80,000 to 1,40,000 genes. Almost all (99.9 per cent) nucleotide bases are exactly the same in all people.
• The functions are unknown for over 50 per cent of the discovered genes.
• Less than 2 per cent of the 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, sometimes hundred to thousand times. They are thought to have no direct coding functions, but they shed light on chromosome structure, dynamics and evolution.
• Chromosome 1 has most genes (2968), and the Y has the fewest (231).
• Scientists have identified about 1.4 million locations where singlebase DNA differences (SNPs – single nucleotide polymorphism, pronounced as ‘snips’) occur in humans. This information promises to revolutionise the processes of finding chromosomal locations for disease-associated sequences and tracing human history.

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By Team Learning Mantras