Class 12 Biology Molecular Basis of Inheritance Human genome project

Human genome project

  • The scientific project which deal with the study of base sequences of DNA molecules of complete set of chromosomes is called human genome project.
  • HGP was closely associated with the rapid development of a new area in biology called as
  • 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.


  • To identifying all the genes that expressed as RNA referred to as Expressed Sequence Tags (ESTs).
  • 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 is called as Sequence Annotation.
  • The total DNA from a cell is isolated and converted into random fragments of relatively smaller sizes and cloned in suitable host using specialised vectors.
  • The cloning resulted into amplification of each piece of DNA fragment.
  • The commonly used vectors are BAC (bacterial artificial chromosomes), and YAC (yeast artificial chromosomes).
  • The fragments were sequenced using automated DNA sequencers.
  • Specialized computer based programmes were developed for the alignment of the sequences.
  • The sequences were subsequently annotated and were assigned to each chromosome.
  • The sequence of chromosome 1 was completed only in May 2006.


Automated DNA sequencer 

Salient Features of Human Genome

  • The human genome contains 3164.7 million nucleotide bases.
  • The average gene consists of 3000 bases with the largest known human gene being dystrophin at 2.4 million bases.


The largest known human gene- dystrophin 

  • The total number of genes is estimated at 30,000.
  • 9 per cent nucleotide bases are exactly the same in all people.
  • The functions are unknown for over 50 per cent of 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.
  • Chromosome 1 has most genes (2968), and the Y has the fewest (231).
  • Scientists have identified about 1.4 million locations where single base DNA differences (SNPs – single nucleotide polymorphism) occur in humans.


Single nucleotide polymorphism (self-drawn )

Applications of HGP

  • All the genes in a genome can be studied together.
  • Helps to understand how tens of thousands of genes and proteins work together in interconnected networks.
  • Helps to diagnose and treat genetic diseases.

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