6.9.1 Salient Features of Human Genome

Some of the salient observations drawn from human genome project are as follows:

  • The human genome contains 3164.7 million nucleotide bases.
  • 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 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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