An international consortium has finished reading the entire genetic code of chromosome 21, the smallest human chromosome. It is the second human chromosome to be completely decoded, following the deciphering of chromosome 22 last December. The scientists, from Japan, Germany, France, Switzerland, the USA and the UK, will publish their results in this week's issue of Nature.
The researchers say that chromosome 21 has around 225 genes, 98 of which were previously unknown. Using this information, and the fact that chromosome 22 has 545 genes, the authors estimate the total number of human genes may be as few as 40,000. Previous estimates have ranged from 50,000 to over 100,000.
The achievement will help researchers seeking to understand Down syndrome, which is caused by an extra copy of chromosome 21. Dr Roger Reeves, who works on the condition, says that 'defining the players and the playing field is a very major step that the Down syndrome community has been working towards for years.'
The findings will also help scientists working on five genetic conditions caused by single, faulty genes known to lie somewhere on chromosome 21. Much less work will now be needed to pinpoint the genes responsible, says Reeves.
Meanwhile, the Human Genome Project released a statement on Monday, saying it had started the final phase of sequencing the three billion base-pairs of, DNA that make up the entire human genetic code. The researchers expect to have a 90 per cent complete 'rough draft' of the human genome finished by mid-June. The US firm Celera Genomics is also expected to assemble its own version of the genome within the next couple of months.
Eric Lander, director of the MIT Center for Genome Research, Boston, is critical of the way the private and public efforts to sequence the human genome have been depicted as a race. 'The whole finishing line mentality is silly' he says. An editorial in this week's Nature also warns against portraying biology's biggest project as a scientific 'Wacky Races'.