Human Genome Project

The Human Genome Project (HGP) was an international effort to sequence the entire set of human DNA and identify all its genes. One of its most striking findings was that the human genome contains only about 20,000 to 25,000 genes, far fewer than the 80,000 to 1,40,000 that scientists had originally predicted. The option of about 1,00,000 reflects this earlier overestimate, which the project disproved. The figure of 3 billion is incorrect as a gene count; it actually refers to the approximate number of base pairs (nucleotide pairs) in the human genome, not the number of genes. The value 5,000 is far too low and corresponds more closely to simple microbial genomes, not the human one. The relatively small gene number revealed that complexity in humans arises largely from alternative splicing and regulation rather than sheer gene count. As detailed in NCERT Class 12, Chapter 6 (Molecular Basis of Inheritance), the HGP also found that less than 2 percent of the genome codes for proteins. As a consistency check, distinguishing gene count (around 25,000) from base-pair count (around 3 billion) confirms 20,000 to 25,000 as the correct gene estimate.