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Fri 22 Oct, 2004 11:47 pm
The New York Times reports:
(Full story here:
http://www.nytimes.com/2004/10/21/science/21gene.html?ex=1256184000&en=dd64aed0bfe5fb8e&ei=5088&partner=rssnyt )
Human Gene Total Falls Below 25,000
By NICHOLAS WADE
Published: October 21, 2004
new and perhaps final report from the international consortium of laboratories that decoded the human genome has revised the estimated number of human genes sharply downward.
About 20,000 human genes have been identified, and up to 5,000 more may await discovery, the group is reporting today in the journal Nature. This tally is considerably less than the 30,000 or so predicted by the consortium and its commercial rival, Celera, when they first described their draft genome sequences in February 2001.
The 30,000 figure was itself a surprising downgrade from the 100,000 human genes commonly said to exist as recently as five years ago, before the exact sequence of DNA units in the genome was decoded.
Coincidentally, French researchers are reporting in the same issue of Nature that they have decoded the genome of a biologically important fish, the spotted green pufferfish. They say it has 20,000 to 25,000 genes, the identical range now estimated for humans.
How can it be that humans, seen by some as the apotheosis of creation, have the same number of genes?
The question is the more pressing because genes are subject to a rigorous "use it or lose it" rule. Those not vital to an organism are quickly rendered useless by mutations. Also, the human brain seems particularly dependent on genetic complexity, because about half of all human genes are active in brain tissue.
From the fishes' point of view, the problem may seem rather less acute. Their large number of genes "may relate to the fact that fish today are one of the most successful families of vertebrate on earth," Dr. Hugues Roest Crollius of the French team said. Along with Dr. Jean Weissenbach and colleagues, Dr. Crollius is reporting that sometime after 450 million years ago, when the ancestors of people and pufferfish took separate evolutionary paths, the puffer and most other fish doubled up their genome in some freak cellular accident.
Though some duplicate genes were shed, many were put to alternative uses, giving fish a special evolutionary advantage. Humans have enjoyed no such doubling in the last half billion years, Dr. Crollius said.....
First of all it is my understanding that there is still an argument in some quarters on just what constitutes a gene on the molecular level. The definition can effect the number of genes counted so I suspect this number will be continuously revised for a while.
Yeppers - heehee - seems some of us get upset if theirs is bigger than ours?
Their genome bigger than ours - or even the same size.
Last I heard was the archaic figure of 100,000...so, I am pretty shocked! Thanks for posting
Size does not matter but numbers do. Look, I'm in my office right now. The microbiology labs are on the same floor in this building. If I were to draw a straight line from my chair across the hall, experiments similar to those described in the Times article are taking place with 75 feet of where I am sitting. (those labs run 24/7) As they post their published articles on the bulletin boards in the hall, I have a general idea of what they are doing. Right now at least one of the programs ongoing is comparing a set of genes in four species H. sapiens (us) Mus musculus (mouse) Monodelphis domesticus (a marsupial) and a species of fish from the genus Posciloposis (I haven't a clue). When you do this just exactly what a gene is becomes significant. Where it start on the chromosome, where it stops, the number of "letters" in the gene is important. This did not used to be an issue because until recently we could not do much of anything with them. But now we can so an exact definition is crucial.. That is why the number in the human genom (and others) keep changing.
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