At a glance: Genetic code

At a glance: Genetic code
Sunday, 11 February, 2001

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)