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Sunday, 11 February, 2001, 16:01 GMT
At a glance: Genetic code
Human chromosomes
There are about 30,000 genes on our 46 chromosomes
The publication of the human genetic code crowns a decade-long endeavour by scientists. Here are the highlights of their findings:
  • There are 3.1 billion letters in the DNA code in every one of the 100 trillion cells in the human body

  • The four nitrogenous bases of the DNA alphabet, represented by the letters A, C, G and T and arranged in pairs, carry the instructions for making all organisms. Each block of three letters corresponds to a single amino acid

  • There are 20 different building blocks (amino acids) used in an array of combinations to produce proteins as different as keratin in hair and haemoglobin in blood

  • Humans have far fewer genes than expected at 30,000 to 40,000, compared to the nematode worm with 18,000 and the fruit fly with 13,000

  • The difference between humans and fruit flies or worms is that human genes work differently and we have more control genes

  • Hundreds of genes appear to have come from bacteria, one of which is a major pathway for depression

  • Most mutations occur in males

  • Scientists are beginning to discover the purpose of the 97% of DNA that does not encode instructions for making proteins. They suspect the so-called "junk DNA" may help to move genes around

  • There are six feet of DNA in each of our cells packed into a structure only 0.0004 inches across.

  • If all of the DNA in the human body were put end to end, it would reach to the Sun and back more than 600 times

  • The information would fill a stack of paperback books 200 feet (60 metres) high, or 200 500-page telephone directories

  • Between humans, DNA differs by only 0.2%, or 1 in 500 bases (letters)

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11 Feb 01 | Science/Nature
06 Oct 00 | Science/Nature
05 Jan 01 | Science/Nature
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