Chinese scientists announced recently that they have discovered a novel mechanism in the genesis of genes, the building blocks of all organisms on Earth. Their research shows genes are continuously created and altered through a process known as gene fission.
The new genes originate by copying their ancestral gene, which partially degenerates during the process, according to the researchers.
This finding confirmed a hypothesis long held by biologists that duplication is one of the major ways for genes to evolve.
Their gene genesis mechanism also suggests that the genome of the fruit fly, the living organism their research is based on, is highly flexible and that even seemingly fixed genes are constantly evolving. Genome refers to the totality of all the genes in the chromosomes of an organism.
This research was done by an international team involving Chinese and American scientists and the finding was published in the latest issue of the scientific journal Nature.
Biologists have been curious about the origin and evolutionary history of genes ever since two US researchers discovered their key role in shaping life 50 years ago.
It has been found that different organisms vary greatly in the number of genes contained in their chromosomes, suggesting the origination of new genes and their evolution is the fundamental issue in the evolution of life, said Wang Wen, a researcher at the Kunming Institute of Zoology under the Chinese Academy of Sciences.
Understanding of the mechanism underlying that process may not enrich our knowledge about all forms of life on Earth, but may contribute to the development of new drugs, Wang said.
Yet most genes were created so long ago that many mutations occurred during their evolutionary process, making it very difficult to figure out their early history. "That's why discussion over this issue has long been on a theoretic basis," he added.
Wang and his colleagues then looked for young genes -- those that had originated within the last one to two million years -- to observe the early stages of gene creation.
The researchers identified a group of genes in three subspecies of the fruit fly that diverged less than a million years ago.
Each subspecies has a parental gene sequence on one chromosome and different numbers of new copies on different chromosomes.
The new copies are very young genes in evolutionary terms -- some of which are the youngest ever discovered -- and so all the intermediate steps from the original parental sequence to the newest copies are visible, according to the researchers.
They named the gene family "monkey king," after the mythical Chinese hero who can transform his hairs into offspring.
They observed that one single ancestral gene in the family -- containing two functional domains - duplicated to produce a copy that lacks partial segments that function to encode proteins.
"One domain in the ancestral gene degenerates, then the new, degenerate gene duplicates, and that also degenerates and destroys the other domain," said Long Banyuan, another researcher involved in the discovery.
Their discovery has thus shed new light on the classic model of gene duplication that suggests the whole gene is duplicated intact without degenerations, Wang said.
Another interesting aspect of the discovery is that it shows genes may not necessarily follow the evolutionary process from the simple to the complex, as previous hypotheses hold.
Their observations of the monkey king gene groups found that the new gene copies appeared to be simpler than the ancestral one.
"When people think about evolution, they intuitively expect it to take some sort of direction towards more complexity -- that is, multi-domain proteins with more complex functions," said Berend Snel, from the Center for Molecular and Bimolecular Informatics at the University of Nijmegen in the Netherlands.
"Sometimes, there's no such direction. That's why gene fission, I think, has been overlooked by some people," he commented.
Wang and his colleagues have been leading in the world in the search for young genes and so far have identified scores of such genes, including the first RNA gene discovered, the sphinx.
(China Daily April 20, 2004)
