First look at human genome shows how little there is
(UPDATE: New throughout, pvs London, changes byline)
By Maggie Fox, Health and Science Correspondent
WASHINGTON, Feb 11 (Reuters) - The first in-depth look at the human genetic code has revealed much less than
anticipated -- about half to a third the number of expected genes, scientists will announce on Monday.
They said their findings so far made it clear that far from being a blueprint, the human genetic code was only a guidepost. The
true directions for what makes a human being lie not in letters of code but in what the body does with that code.
They have found a few interesting tidbits.
Most of the variation -- the mutations that underlie evolution and bring gradual change -- is on the Y chromosome. That means
men are responsible for most mutations, because only men have a Y chromosome.
They have also confirmed that there is no genetic basis for what people describe as race, and found only a few small differences
set one person apart from another.
``You and I differ by 2.1 million genetic letters from each other,'' Craig Venter, chief scientific officer at Celera Genomics Inc.
(NYSE:CRA - news), which carried out one of the two studies being published, said in a telephone interview.
``Probably only a few thousand of those differences account for the biological differences between us, which means we all are
essentially identical twins -- even more than I thought.''
RACE IS 'NOT A SCIENTIFIC CONCEPT'
Celera used DNA from five volunteers -- three women and two men, ethnically African-American, Chinese, Hispanic and
white.
``You can clearly tell the females from the males because of the X and Y chromosomes, but race is not a scientific concept,''
Venter said.
The future, both teams of researchers say, lies in understanding the proteins that make up people and not so much the genes
that control production of the proteins. This infant scientific field is known as proteomics.
``There are about 30,000 to 40,000 protein-coding genes in the human genome -- only about twice as many as in worm or
fly,'' members of the International Human Genome Sequencing Consortium, the public effort, wrote in their report.
``However, the genes are more complex, with more alternative splicing generating a larger number of protein products,'' they
added in their report, to be published in next week's issue of the journal Nature.
In other words, the proteins for which genes code can be mixed and matched to make even more, just as the primary colors --
yellow, red and blue -- can be mixed to make a myriad of colors.
Rockville, Maryland-based Celera finds a similar number in its own, separate analysis, published in the journal Science --
somewhere between 26,383 and 39,114.
Originally, scientists thought there were about 100,000 human genes, but in recent years revised that downward to between
60,000 and 80,000.
The two studies were to be released on Monday as part of a carefully coordinated and controlled announcement. But British
Sunday newspapers broke the careful embargo, so the material was released on Saturday night.
Researchers said they were surprised to find so few genes.
``On the one hand, this is spectacular news because it means we have only a third as many proteins to understand,'' Eric
Lander, head of genome sequencing at the Whitehead Institute at the Massachusetts Institute of Technology (MIT), said in a
telephone interview.
``On the other hand, we may feel we have set ourselves a larger problem. Although there are fewer components, they fit
together in more complex ways,'' added Lander, whose lab did much of the work in the public effort.
``If anyone found the basis for the pride of our species in the number of genes we had, they may have to rethink it.''
Venter agrees. ``There are only a few hundred genes that we have in the human genome that are not in the mouse genome,'' he
said.
IT'S NOT A BLUEPRINT
``In fact, what has been said about the human genome, that it is the blueprint for humans, it's not true. We don't think blueprint
is the right metaphor.''
Both teams had announced jointly last June that they had sequenced the human genome -- 3.1 billion base pairs, the rungs that
make up the ladder-like double helix of DNA. But all they had was a repetitive readout of A's, C's, T's and G's, the nucleotides
that pair up.
They did not know what that code said.
Eight months later, they have done the first analysis and have found what they believe to be a history of human evolution. The
changes that made humans a little different from other animals had been preserved, Lander said.
``In June, maybe people thought we had this big pile of letters and it was all stuff,'' Lander said. ``But I don't know if people
realize that we just found the world's greatest history book. We are going to be up every night reading tales from the genome.
It's so cool.'' |
